JP2002103054A - Method for spot welding of high strength steel plate - Google Patents
Method for spot welding of high strength steel plateInfo
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- JP2002103054A JP2002103054A JP2000299942A JP2000299942A JP2002103054A JP 2002103054 A JP2002103054 A JP 2002103054A JP 2000299942 A JP2000299942 A JP 2000299942A JP 2000299942 A JP2000299942 A JP 2000299942A JP 2002103054 A JP2002103054 A JP 2002103054A
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、高強度鋼板のスポ
ット溶接において、溶接部の引張強さ、疲労強度を向上
させるためのスポット溶接方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding method for improving the tensile strength and fatigue strength of a weld in spot welding of a high strength steel sheet.
【０００２】[0002]
【従来の技術】近年、自動車の安全対策のため、また低
燃費対策やＣＯ2排出量削減対策のため、自動車の車体
に高強度鋼板を使用する必要性が高まっている。自動車
の車体組み立てにおいては、スポット溶接が主に用いら
れており、高強度鋼板の溶接においてもスポット溶接が
主に用いられている。スポット溶接部の品質指標とし
て、引張せん断強さ（継手のせん断方向に引張荷重を負
荷したときの引張強さ）、十字引張強さ（継手の剥離方
向に引張荷重を負荷したときの引張強さ）、疲労強度
（継手のせん断、剥離方向に繰り返し荷重を負荷したと
きの疲労強度）などが重要である。2. Description of the Related Art In recent years, there has been an increasing need to use high-strength steel sheets for automobile bodies for safety measures of automobiles, fuel saving measures and measures for reducing CO 2 emissions. Spot welding is mainly used in assembling automobile bodies, and spot welding is also mainly used in welding high-strength steel plates. Tensile shear strength (tensile strength when a tensile load is applied in the shear direction of the joint) and cross tensile strength (tensile strength when a tensile load is applied in the peel direction of the joint) ), Fatigue strength (fatigue strength when a load is repeatedly applied in the direction of joint shear and peeling) are important.
【０００３】高強度鋼板のスポット溶接部の引張せん断
強さに関しては、鋼板の引張強さが増加するとともに引
張せん断強さも増加する傾向にある。しかし、継手の十
字引張強さは、鋼板の引張強さが増加してもわずかに増
加するだけであり、成分によっては逆に低下する場合も
ある。例を上げるなら、引張強さが２９０ＭＰａの軟鋼
板の代わりに、引張強さが５９０ＭＰａの高強度鋼板を
用いれば、スポット溶接継手の引張せん断強さはほぼ２
倍になるが、十字引張強さはほとんど増加せず、下記
（１）式で示される炭素当量Ｃｅｑの値が０．２０を越
える高強度鋼板を用いた場合には、むしろ軟鋼を用いた
場合より低い値を示す場合がある。 Ｃｅｑ＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋２Ｐ＋４Ｓ ・・（１） （式中、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓは、それぞれ鋼中の炭
素、シリコン、マンガン、リン、硫黄の含有量（質量
％）を示す。）[0003] Regarding the tensile shear strength of a spot welded portion of a high-strength steel sheet, the tensile shear strength tends to increase as the tensile strength of the steel sheet increases. However, the cross tensile strength of the joint increases only slightly with an increase in the tensile strength of the steel sheet, and may be reduced depending on the component. For example, if a high-strength steel plate having a tensile strength of 590 MPa is used instead of a mild steel plate having a tensile strength of 290 MPa, the tensile shear strength of the spot welded joint is almost 2
Although it is twice as large, the cross tensile strength hardly increases, and when using a high-strength steel sheet having a carbon equivalent Ceq value represented by the following formula (1) exceeding 0.20, rather using mild steel May show lower values. Ceq = C + Si / 30 + Mn / 20 + 2P + 4S (1) (where C, Si, Mn, P, and S indicate the contents (% by mass) of carbon, silicon, manganese, phosphorus, and sulfur in the steel, respectively. )
【０００４】一般的に、鋼板の引張強さが増加するほど
Ｃｅｑは高い値となるため、鋼板の高強度化に伴い、十
字引張強さは軟鋼より低い値を示すようになる。このよ
うに、炭素当量Ｃｅｑの増加とともに十字引張強さが低
下するのは、炭素当量の増加とともにナゲット（溶接）
部と熱影響部の硬さが増加し、靱性が低下して破壊が容
易に起こりやすくなるからであると考えられている。特
に、十字引張強さの場合には、ナゲット周辺部での応力
集中が激しいので、この影響は顕著になり、溶接部と熱
影響部の硬さが高い値を示す場合には、十字引張強さは
低い値を示す。Generally, as the tensile strength of a steel sheet increases, the value of Ceq becomes higher. Therefore, as the steel sheet becomes stronger, the cross tensile strength becomes lower than that of mild steel. The reason why the cross tensile strength decreases as the carbon equivalent Ceq increases is that the nugget (welding) increases as the carbon equivalent increases.
This is considered to be because the hardness of the heat-affected zone and the heat-affected zone increases, the toughness decreases, and fracture easily occurs. In particular, in the case of the cross tensile strength, the stress concentration around the nugget is severe, so this effect is remarkable, and when the hardness of the welded portion and the heat affected zone show a high value, the cross tensile strength is high. Indicates a low value.
【０００５】一般的にナゲット径が大きい場合には，破
壊はナゲットの周囲で起こるが、Ｃｅｑが高い場合には
亀裂が一部ナゲットの中にも入り破断が起こる。従っ
て、ナゲット内および熱影響部の硬さは継手強度に大き
な影響を及ぼす。[0005] In general, when the diameter of the nugget is large, the fracture occurs around the nugget. However, when the Ceq is high, a crack partially enters the nugget and breaks. Therefore, the hardness of the inside of the nugget and of the heat-affected zone greatly affects the joint strength.
【０００６】スポット溶接部の疲労強度も、十字引張強
さと同様、鋼板の引張強さが増加してもほとんど増加し
ない。例を上げるなら、引張強さが２９０ＭＰａの軟鋼
板の代わりに、引張強さが５９０ＭＰａの高強度鋼板を
用いても、引張せん断方向に荷重を負荷した場合の疲労
強度、例えば、応力負荷の回数が２×１０6回における
荷重を疲労強度と定義すると、疲労強度は２倍にはなら
ず軟鋼板の場合とほぼ同じ値を示すのである。これは、
剥離方向に荷重を負荷した場合にも同様である。剥離方
向に負荷した場合には、先にも述べたように、ナゲット
周辺部での応力集中が激しいので、せん断方向に負荷し
た場合に比べ、疲労強度は一桁ほど低い値となる。この
ように、疲労強度が低い値を示す原因としては、従来、
報告されているように、スポット溶接部のノッチ形状が
考えられる。すなわち、図１で示したように、鋼板１の
間に存在するナゲット２の部分がノッチ形状になってい
るため、引張せん断方向（矢印方向）３に負荷されて疲
労試験を行った場合、引張強さの高い鋼板を用いても、
このノッチ効果によって疲労強度が向上しないのであ
る。特に、高強度鋼板を用いた場合には、軟鋼板を用い
た場合に比べて、ナゲット内と熱影響部の硬さが増加す
るために疲労強度が低下するものと考えられている。[0006] The fatigue strength of the spot welds, like the cross tensile strength, hardly increases even if the tensile strength of the steel sheet increases. For example, instead of a mild steel plate having a tensile strength of 290 MPa, even if a high-strength steel plate having a tensile strength of 590 MPa is used, the fatigue strength when a load is applied in the tensile shear direction, for example, the number of times of stress loading If the load at 2 × 10 6 times is defined as the fatigue strength, the fatigue strength does not double and shows almost the same value as that of the mild steel sheet. this is,
The same applies when a load is applied in the peeling direction. As described above, when the load is applied in the peeling direction, the stress concentration around the nugget is intense, so that the fatigue strength is about one digit lower than when the load is applied in the shear direction. As described above, the cause of the low value of the fatigue strength is conventionally,
As reported, notch shapes in spot welds are possible. That is, as shown in FIG. 1, the portion of the nugget 2 existing between the steel plates 1 has a notch shape. Therefore, when a fatigue test is performed by applying a load in the tensile shear direction (arrow direction) 3, Even if a high strength steel plate is used,
This notch effect does not improve the fatigue strength. In particular, when a high-strength steel sheet is used, it is considered that the fatigue strength is reduced due to an increase in hardness of the inside of the nugget and the heat-affected zone, as compared with the case of using a mild steel sheet.
【０００７】スポット溶接では、通常、溶接通電完了後
も一定時間の間電極を鋼板に接触させたまま保持する。
特に高強度鋼板の溶接においては、スプリングバックを
懸念して通電後の電極保持時間は比較的長く設定される
ことが多い。一方、スポット溶接電極は水冷されている
ため、溶接通電完了後の電極保持中に溶接部から電極に
向けて急速に熱が奪われ溶接部が急冷されるため、特に
高強度鋼板では、溶接部の硬さが増加するものと考えら
れる。[0007] In spot welding, usually, the electrodes are kept in contact with the steel plate for a certain period of time after the completion of welding.
In particular, in welding high-strength steel sheets, the electrode holding time after energization is often set to be relatively long due to concerns about springback. On the other hand, since the spot welding electrode is water-cooled, heat is rapidly taken away from the welding portion toward the electrode during electrode holding after the completion of welding, and the welding portion is rapidly cooled. It is considered that the hardness of the steel increases.
【０００８】「溶接技術」１９８２年３月号の第３４ペ
ージ〜第３８ページにおいては、高強度鋼板のスポット
溶接部におけるＵ字引張強さを改善する目的で、通電完
了後の電極保持時間を短くすることによって溶接部の硬
さを低下させる方法が開示されている。しかし、電極保
持時間を極端に短くすると、ナゲット部が凝固する前に
電極による加圧力が無くなるため、ナゲット部から溶融
金属が飛び出して、ナゲット内で欠陥が発生することと
なる。On pages 34 to 38 of "Welding Technology", March 1982, in order to improve the U-shaped tensile strength at the spot welded portion of a high-strength steel plate, the electrode holding time after the completion of energization is set. A method of reducing the hardness of the weld by shortening it is disclosed. However, if the electrode holding time is extremely short, the pressing force by the electrode is eliminated before the nugget portion solidifies, so that the molten metal jumps out of the nugget portion and a defect occurs in the nugget.
【０００９】「鉄と鋼」第６８巻第９号第１４４４ペー
ジ〜第１４５１ページにおいては、溶接通電が完了した
後、一定時間経過後に再度通電を行い（テンパー通
電）、ナゲット部と熱影響部を焼鈍して硬さを低下さ
せ、残留応力を変化させることにより、スポット溶接部
の疲労強度を向上させる方法が開示されている。「溶接
技術」の同上ページにおいても、溶接通電後の後熱通電
によって溶接部の剥離試験における破断形状および強度
の回復に効果があることが開示されている。しかしこの
方法は、適正な条件の幅が狭いこともあって量産の工場
では実用的ではないと考えられていた。In "Iron and Steel", Vol. 68, No. 9, pp. 1444 to 1451, after the welding energization is completed, energization is performed again after a certain period of time (tempering), and the nugget part and the heat-affected zone A method for improving the fatigue strength of a spot welded part by lowering the hardness by annealing steel and changing the residual stress. The same page of “Welding Technique” also discloses that post-heating after welding is effective in recovering the fracture shape and strength in a peeling test of a welded portion. However, this method was considered to be impractical in mass-production factories due to the narrow range of appropriate conditions.
【００１０】[0010]
【発明が解決しようとする課題】高強度鋼板のスポット
溶接において、溶接部の十字引張強さや疲労強度を改善
することを目的とした従来の技術は、上記のようにいず
れも量産現場で適用するためには十分な安定性を有して
いるとはいえない。In the spot welding of high-strength steel sheets, the conventional techniques aimed at improving the cross tensile strength and fatigue strength of the welded portions are all applied in mass production sites as described above. Therefore, it cannot be said that it has sufficient stability.
【００１１】溶接部の品質を確保するためには、溶接後
の冷却条件を常に一定に保つ必要がある。溶接後の冷却
条件を一定に保つための適正操業条件は鋼板の種類や板
厚によって異なったものとなる。したがって、スポット
溶接を行う鋼板の種類、板厚毎に最適操業条件を見つけ
出す必要があり、製造管理が煩雑であった。In order to ensure the quality of the weld, it is necessary to keep the cooling conditions after welding constant. The proper operating conditions for keeping the cooling conditions after welding constant vary depending on the type and thickness of the steel sheet. Therefore, it is necessary to find out the optimal operating conditions for each type and thickness of the steel plate to be spot-welded, and the production management is complicated.
【００１２】同一のスポット溶接電極を使い続けると、
電極先端の鋼板との接触部は次第に劣化し、電極先端径
が増加する。特に、溶融浸漬法、電気めっき法などで製
造されためっき鋼板（Ｚｎめっき、Ｚｎ−Ｆｅめっき、
Ｚｎ−Ａｌめっき、Ｎｉ−Ｚｎめっき、Ｓｎ−Ｚｎめっ
き、Ｐｂ−Ｓｎめっき、など）を連続打点する場合に
は、打点数の増加に伴ってめっきと電極との合金化反応
によって電極先端の合金層が脱落し、電極先端径が増加
する。冷延鋼板の連続打点溶接では電極使用回数１５０
００回程度以上で、めっき鋼板の連続打点溶接では電極
使用回数５００回程度で電極先端が劣化し、電極先端径
が増加する。電極先端径が増加すると電極と鋼板との接
触面積も増加し、鋼板中における電流通過断面積も増大
するため、同一電流を流している場合には電流密度が低
下して通電状況が変化することとなる。If the same spot welding electrode is continuously used,
The contact portion of the electrode tip with the steel plate gradually deteriorates, and the electrode tip diameter increases. In particular, plated steel sheets (Zn plating, Zn-Fe plating,
(Zn-Al plating, Ni-Zn plating, Sn-Zn plating, Pb-Sn plating, etc.) in the case of continuous spotting, the alloy at the tip of the electrode by an alloying reaction between the plating and the electrode as the number of spots increases The layers fall off and the electrode tip diameter increases. 150 times of electrode use in continuous spot welding of cold rolled steel sheets
At about 00 times or more, in continuous spot welding of a plated steel sheet, the electrode tip deteriorates and the electrode tip diameter increases about 500 times the electrode is used. When the electrode tip diameter increases, the contact area between the electrode and the steel plate also increases, and the current passage cross-section in the steel plate also increases.Therefore, when the same current is flowing, the current density decreases and the conduction state changes. Becomes
【００１３】高強度鋼板のスポット溶接部の品質改善を
目的として、従来知られているように通電完了後の電極
保持時間を短縮したり、あるいは溶接通電後の後熱通電
によって溶接部の冷却速度を調整する方法においては、
電極保持時間あるいは後熱通電条件として適正条件を確
認するために、例えば新品の電極を用いて品質評価試験
を行う。ところが、上記のように電極は使用とともに劣
化して電流条件が変化するため、新品の電極においては
適正条件であったものが、劣化が進んだ電極では同一の
製造方法であっても適正条件から外れることとなる。こ
のため、高強度鋼板のスポット溶接において、従来は電
極の使用期間全体にわたって溶接部の品質を確保するこ
とができなかった。For the purpose of improving the quality of a spot welded portion of a high-strength steel plate, as is conventionally known, the electrode holding time after completion of energization is reduced, or the cooling rate of the welded portion is increased by post-heating after energization. In the method of adjusting
For example, a quality evaluation test is performed using a new electrode in order to confirm an appropriate condition as an electrode holding time or a post-heating condition. However, as described above, the electrode deteriorates with use and the current conditions change, so that the new electrode had the appropriate conditions, but the deteriorated electrode had the same manufacturing method, but the same condition was not satisfied. It will come off. For this reason, in spot welding of a high-strength steel plate, conventionally, it was not possible to ensure the quality of the welded portion over the entire use period of the electrode.
【００１４】本発明は、高強度鋼板のスポット溶接にお
いて、溶接部の十字引張強さや疲労強度が優れた溶接方
法の提供に関し、量産現場で適用することのできる安定
性を有した溶接方法を提供することを第１の目的とし、
鋼種や板厚が異なる鋼板の溶接や、溶接電極の先端条件
が変化した場合における溶接においても溶接部の品質を
確保することのできる溶接方法を提供することを第２の
目的とする。The present invention relates to a method for spot welding of high-strength steel sheets, which provides a welding method with excellent cross-tensile strength and fatigue strength at a welded portion, and provides a stable welding method applicable to mass production. With the primary purpose of doing
It is a second object of the present invention to provide a welding method capable of ensuring the quality of a welded portion even in welding of steel plates having different steel types and plate thicknesses and in welding when the tip condition of a welding electrode changes.
【００１５】[0015]
【課題を解決するための手段】溶接電流、通電時間、通
電終了後の電極を離す時間等の溶接条件を一定に保って
も、溶接する鋼板の種類や板厚が変わったり、また電極
が劣化して電極と鋼板との接触面積が変化したりした場
合は、溶接前後における溶接部の温度履歴が変動し、そ
の結果として溶接部の品質に変化が及ぶこととなる。と
ころで、溶接中における溶接部の温度実績が推定できれ
ば、この温度実績が常に一定になるように溶接条件を変
更することによって、たとえば鋼種、板厚や電極条件に
変更が生じたとしても溶接部の温度履歴を一定に保つこ
とができる。溶接中における溶接部の温度実績を実測す
ることは非常に困難であるが、溶接部より観測可能な物
理量を検出し、検出した物理量を用いて熱伝導モデルに
よる数値解析を行なうことによって必要な精度で溶接部
の温度履歴を計算で求めることができるのであれば、こ
の温度を用いて溶接条件にフィードバックを行なっても
よい。Means for Solving the Problems Even when welding conditions such as a welding current, an energizing time, and a time for separating an electrode after the energization are kept constant, the type and thickness of a steel plate to be welded are changed or the electrode is deteriorated. If the contact area between the electrode and the steel sheet changes, the temperature history of the weld before and after welding changes, and as a result, the quality of the weld changes. By the way, if the actual temperature of the weld during welding can be estimated, the welding conditions are changed so that the actual temperature is always constant. The temperature history can be kept constant. It is very difficult to actually measure the actual temperature of the weld during welding, but the required accuracy can be obtained by detecting physical quantities observable from the weld and performing a numerical analysis with a heat conduction model using the detected physical quantities. If the temperature history of the welded portion can be obtained by calculation, the temperature may be used to feed back welding conditions.
【００１６】本発明は、観測可能な物理量として溶接電
流、電極間電圧、および材料物性値として鋼板の固有抵
抗、熱伝導度や板厚などを用い、熱伝導モデルによる数
値解析を行なえば、十分な精度と十分な速度で溶接部の
任意の位置における各時刻毎の温度を計算で求めること
ができる点に着目し、この温度を用いてオンラインで溶
接条件を微調整することにより、たとえ鋼板の種類や板
厚、電極条件が変化しても常に一定の溶接部温度履歴を
実現することができ、高強度鋼板のスポット溶接におい
て、安定して良好な溶接部品質を得ることができた。According to the present invention, it is sufficient if a numerical analysis using a heat conduction model is performed by using a welding current and an inter-electrode voltage as observable physical quantities and a specific resistance, a thermal conductivity and a thickness of a steel sheet as material property values. Focus on the fact that it is possible to calculate the temperature at each point in the weld at any time with high accuracy and sufficient speed, and by using this temperature to fine-tune the welding conditions online, Even when the type, plate thickness, and electrode conditions change, a constant weld temperature history can be always realized, and in spot welding of high-strength steel plates, stable and good weld quality can be obtained.
【００１７】本発明の第１は、高強度鋼板のスポット溶
接方法において、スポット溶接時の電流と電極間電圧を
計測し、計測した電流と電極間電圧および材料物性値を
用いた計算を行い、溶接通電終了後の冷却中に前記計算
結果に基づいて、電極を鋼板から離す時期の決定、溶接
通電終了後に継続する後通電における後通電電流と後通
電時間の調整、溶接通電が終了した後冷却しその後開始
した後通電における後通電電流と後通電時間の調整、電
極加圧力の調整のうちの１又は２以上を行うことを特徴
とする高強度鋼板のスポット溶接方法である（請求項
１）。According to a first aspect of the present invention, in a spot welding method for a high-strength steel sheet, a current and a voltage between electrodes during spot welding are measured, and a calculation is performed using the measured current, a voltage between electrodes, and material properties. Based on the above calculation results during the cooling after the end of the welding current, the timing of separating the electrode from the steel plate, the adjustment of the after-current and the post-current time in the after-current that is continued after the completion of the welding current, and the cooling after the welding is completed. And a method for spot welding a high-strength steel plate, wherein one or more of adjustment of a post-current and a post-current in a post-current after starting and adjustment of an electrode pressing force are performed. .
【００１８】電極の経時変化によって電極と鋼板との接
触面積が変化したとき、鋼板中の通電面積Ｓが変化す
る。一方、通電電流と電極間電圧とから電極間抵抗を求
めることができ、電極間抵抗と鋼板の板厚、鋼板の固有
抵抗から通電面積Ｓを求めることができるのである。そ
して、これらの値を用いることによって、鋼板中の通電
部位における単位体積あたりの発熱量が定まる。従っ
て、溶接通電中の通電電流と電極間電圧とを計測するこ
とにより、電極と鋼板、鋼板同士の接触状況をある程度
推定することができるので、この推定結果に基づいて電
極を鋼板から離す時期の決定、溶接通電終了後に継続す
る後通電における後通電電流と後通電時間の調整、溶接
通電が終了した後冷却しその後開始した後通電における
後通電電流と後通電時間の調整、電極加圧力の調整のう
ちの１又は２以上を行えば、たとえ電極の経時変化があ
ってもその経時変化に対応して溶接時の熱履歴条件を一
定に保つことが可能であり、溶接品質を安定して良好に
保つことができる。When the contact area between the electrode and the steel plate changes due to the aging of the electrode, the current-carrying area S in the steel plate changes. On the other hand, the interelectrode resistance can be obtained from the energizing current and the interelectrode voltage, and the energized area S can be obtained from the interelectrode resistance, the thickness of the steel sheet, and the specific resistance of the steel sheet. Then, by using these values, the heat value per unit volume at the energized portion in the steel sheet is determined. Therefore, by measuring the current flowing during welding and the voltage between the electrodes, it is possible to estimate the contact state between the electrode and the steel sheet or between the steel sheets to some extent. Decision, adjustment of post-energization current and post-energization time in post-energization that continues after the end of welding energization, adjustment of post-energization current and post-energization time in energization after cooling after welding energization ends, and adjustment of electrode pressing force By performing one or more of the above, even if the electrode changes with time, it is possible to keep the heat history condition at the time of welding constant in accordance with the change with time, and to stably improve the welding quality. Can be kept.
【００１９】本発明の第２は、上記第１の発明における
計測した電流と電極間電圧および材料物性値を用いた計
算は、熱伝導モデルに基づいた数値計算によりスポット
溶接部の任意の位置における各時刻毎の温度を求める数
値計算であることを特徴とする上記高強度鋼板のスポッ
ト溶接方法である（請求項２）。According to a second aspect of the present invention, the calculation using the measured current, the electrode-to-electrode voltage, and the material properties in the first aspect of the present invention is performed by a numerical calculation based on a heat conduction model at an arbitrary position of the spot weld. A spot welding method for a high-strength steel plate, characterized in that it is a numerical calculation for obtaining a temperature at each time (claim 2).
【００２０】上記のように、観測可能な物理量として溶
接電流、電極間電圧、および材料物性値として鋼板の固
有抵抗、熱伝導度や板厚などを用い、熱伝導モデルによ
る数値解析を行なえば、十分な精度と十分な速度で溶接
部の任意の位置における各時刻毎の温度を計算で求める
ことができる。この温度を用いてオンラインで溶接条件
（電極を鋼板から離す時期の決定、溶接通電終了後に継
続する後通電における後通電電流と後通電時間の調整、
溶接通電が終了した後冷却しその後開始した後通電にお
ける後通電電流と後通電時間の調整、電極加圧力の調整
のうちの１又は２以上）を微調整することにより、たと
え鋼板の鋼種や板厚、電極条件が変化しても常に一定の
溶接部温度履歴を実現することができ、高強度鋼板のス
ポット溶接において、安定して良好な溶接部品質を得る
ことができるのである。As described above, if a numerical analysis using a heat conduction model is performed by using a welding current and an inter-electrode voltage as observable physical quantities and a specific resistance, a thermal conductivity and a thickness of a steel sheet as material property values, The temperature at each time at an arbitrary position of the welded portion can be obtained by calculation with sufficient accuracy and sufficient speed. Using this temperature, online welding conditions (determination of the time to separate the electrode from the steel plate, adjustment of the post-current and post-current in post-current after the end of welding,
After the completion of the welding current, the cooling is performed, and then the cooling is started. Then, one or two or more of the adjustment of the post-current and the post-current during the current application, and the adjustment of the electrode pressing force are finely adjusted. Even if the thickness and the electrode conditions change, a constant weld temperature history can be always realized, and in the spot welding of a high-strength steel sheet, a good weld quality can be stably obtained.
【００２１】本発明の第３は、高強度鋼板のスポット溶
接方法において、スポット溶接時の電流と電極間電圧を
計測し、計測した電流と電極間電圧および材料物性値を
用いて熱伝導モデルに基づいた数値計算からスポット溶
接部の任意の位置における各時刻毎の温度を求め、溶接
通電終了後の冷却中に前記求めた温度に基づいて電極を
鋼板から離す時期を定めることを特徴とする高強度鋼板
のスポット溶接方法である。電極を鋼板から離す時期の
決定については、溶接通電終了後の冷却中にスポット溶
接部の特定の位置における前記温度が予め定めた所定温
度より低下したら電極を鋼板から離すと好ましい。スポ
ット溶接部の特定の位置はナゲット中心部であり、予め
定めた所定温度は鋼板の凝固温度とするとより好ましい
（請求項２、３、４）。A third aspect of the present invention is a method for spot welding a high-strength steel sheet, in which a current and a voltage between electrodes during spot welding are measured, and the measured current, a voltage between electrodes, and material properties are used to form a heat conduction model. Determining a temperature at each time at an arbitrary position of the spot weld from the numerical calculation based on the time, and determining a timing of separating the electrode from the steel plate based on the determined temperature during cooling after the end of welding power supply. This is a spot welding method for high strength steel sheets. Regarding the timing of separating the electrode from the steel plate, it is preferable that the electrode be separated from the steel plate when the temperature at a specific position of the spot welded portion falls below a predetermined temperature during cooling after the end of the welding current. The specific position of the spot weld is the center of the nugget, and it is more preferable that the predetermined temperature is the solidification temperature of the steel sheet (claims 2, 3, and 4).
【００２２】通電完了後の電極保持時間を短くすること
によって溶接部の硬さを低下させ、高強度鋼板のスポッ
ト溶接部の品質を改善する点が従来から知られている。
本発明においては、通電完了後の電極保持時間を一定と
するのではなく、溶接通電終了後の冷却中において、計
算によって求めた溶接部の温度に基づいて電極を鋼板か
ら離す時期を定めることにより、たとえ鋼種や板厚、電
極劣化等に基づいて電極条件が変化したとしても、常に
最も適切なタイミングで処置を行なうことが可能になっ
た。即ち、電極保持が短すぎてナゲット部から溶融金属
が飛び出すトラブルも発生せず、また電極保持が長すぎ
て溶接部の硬さが上昇するトラブルも発生しない。It is conventionally known that the hardness of the welded portion is reduced by shortening the electrode holding time after the completion of energization, thereby improving the quality of the spot welded portion of a high-strength steel plate.
In the present invention, instead of keeping the electrode holding time after the energization is completed, during cooling after the end of the welding energization, by determining the time to separate the electrode from the steel sheet based on the calculated temperature of the welded part by cooling. Even if the electrode conditions change based on the steel type, plate thickness, electrode deterioration, etc., the treatment can always be performed at the most appropriate timing. That is, there is no trouble that the molten metal jumps out of the nugget portion because the electrode holding is too short, and there is no problem that the hardness of the welded portion increases because the electrode holding is too long.
【００２３】本発明の第４は、高強度鋼板のスポット溶
接方法において、スポット溶接時の電流と電極間電圧を
計測し、計測した電流と電極間電圧および材料物性値を
用いて熱伝導モデルに基づいた数値計算からスポット溶
接部の任意の位置における各時刻毎の温度を求め、溶接
通電終了後も後通電を継続し、冷却中に前記求めた温度
に基づいて後通電電流と後通電時間を調整することを特
徴とする高強度鋼板のスポット溶接方法である。後通電
電流と後通電時間の調整は、スポット溶接部の特定の位
置における冷却時間が予め定めた冷却時間範囲となるよ
うに行うと好ましい。スポット溶接部の特定の位置はナ
ゲット端部から熱影響部端部までの位置であり、予め定
めた冷却時間範囲は凝固温度から１０００℃までの冷却
時間が溶接時間の６０％以上となる範囲であるとすると
より好ましい（請求項２、５、６）。A fourth aspect of the present invention is a method for spot welding a high-strength steel sheet, wherein a current and a voltage between electrodes during spot welding are measured, and a heat conduction model is formed using the measured current, voltage between electrodes and material properties. From the numerical calculation based on the temperature at each point in the spot weld at any time, the post-energization is continued even after the end of welding energization, and the post-energization current and post-energization time are determined based on the determined temperature during cooling. This is a spot welding method for a high-strength steel sheet, which is characterized by adjusting. The adjustment of the post-energization current and the post-energization time is preferably performed such that the cooling time at a specific position of the spot welding portion is within a predetermined cooling time range. The specific position of the spot weld is a position from the end of the nugget to the end of the heat-affected zone, and the predetermined cooling time range is a range where the cooling time from the solidification temperature to 1000 ° C. is 60% or more of the welding time. It is more preferable if there is one (claims 2, 5, and 6).
【００２４】この発明は、溶接通電終了後も後通電を継
続し、それによって溶接完了後の溶接部冷却速度を緩冷
却とする点が特徴である。高強度鋼板の溶接部の品質が
劣化するのは、溶接完了後の溶接部冷却速度が速すぎる
場合である。本発明のように溶接通電終了後に、溶接通
電電流よりも低い電流値で後通電を行なうことにより、
溶接完了後の溶接部冷却速度を遅くすることができ、結
果として溶接部の品質を改善することが可能になった。The present invention is characterized in that the post-energization is continued even after the end of the energization of the welding, thereby slowing down the cooling rate of the weld after the completion of the welding. The quality of the welded part of the high-strength steel sheet is deteriorated when the cooling rate of the welded part after the welding is completed is too high. By performing post-energization at a current value lower than the welding energization current after the end of welding energization as in the present invention,
The cooling rate of the weld after completion of welding can be reduced, and as a result, the quality of the weld can be improved.
【００２５】さらに、後通電電流と後通電時間を一定と
するのではなく、温度計算結果に基づいて後通電電流と
後通電時間を調整する。溶接終了後の溶接部の冷却速度
を速くしすぎると、溶接部の元素の偏析が顕著になって
溶接部品質を劣化させることとなる。一方、溶接部の冷
却速度が遅すぎると、スポット溶接１点あたりの所要時
間が増大し、溶接生産性を悪化させることとなる。本発
明においては、鋼種、板厚、溶接電極の劣化状況に関わ
らず、溶接部の冷却速度を一定に保持することが可能に
なるので、常に溶接部の品質を安定して良好に保つこと
ができると同時に、溶接生産性を低下させることがな
い。Further, the post-energization current and the post-energization time are adjusted based on the temperature calculation result instead of keeping the post-energization current and the post-energization time constant. If the cooling rate of the weld after the end of welding is too high, segregation of elements in the weld becomes significant and the quality of the weld deteriorates. On the other hand, if the cooling rate of the welded portion is too slow, the required time per spot welding point increases, and the welding productivity is deteriorated. In the present invention, the cooling rate of the welded portion can be kept constant irrespective of the steel type, the plate thickness, and the deterioration state of the welding electrode, so that the quality of the welded portion can always be kept stable and good. At the same time, welding productivity is not reduced.
【００２６】本発明の第５は、高強度鋼板のスポット溶
接方法において、スポット溶接時の電流と電極間電圧を
計測し、計測した電流と電極間電圧および材料物性値を
用いて熱伝導モデルに基づいた数値計算からスポット溶
接部の任意の位置における各時刻毎の温度を求め、溶接
通電を終了した後冷却し、その後後通電を開始し、前記
求めた温度に基づいて後通電電流と後通電時間を調整す
ることを特徴とする高強度鋼板のスポット溶接方法であ
る。後通電電流と後通電時間の調整は、スポット溶接部
の特定の位置における前記計算最高到達温度が予め定め
た所定温度範囲内に入るように行うと好ましい。スポッ
ト溶接部の特定の位置はナゲット端部から熱影響部端部
までの位置であり、予め定めた所定温度範囲は５００〜
９００℃とするとより好ましい（請求項２、７、８）。According to a fifth aspect of the present invention, in a spot welding method for a high-strength steel sheet, a current and an inter-electrode voltage during spot welding are measured, and the measured current, an inter-electrode voltage and material properties are used to form a heat conduction model. Based on the numerical calculation based on the temperature at each position in the spot weld, the temperature at each time is determined, cooling is performed after the welding is completed, and then the post-energization is started. This is a spot welding method for a high-strength steel sheet, characterized by adjusting time. The adjustment of the post-energization current and the post-energization time is preferably performed so that the calculated maximum attained temperature at a specific position of the spot welded portion falls within a predetermined temperature range. The specific position of the spot weld is a position from the end of the nugget to the end of the heat-affected zone, and the predetermined temperature range is 500 to
The temperature is more preferably set to 900 ° C. (claims 2, 7, 8).
【００２７】この発明においては、溶接通電終了後に一
度電流を停止し、次いで冷却中に後通電を開始し、この
後通電によって溶接部にテンパー処理を施すものであ
る。この発明の特徴は、温度計算結果に基づいて後通電
電流と後通電時間を調整するので、後通電時の溶接部最
高到達温度を所定の温度範囲内におさめることが可能に
なる。その結果、たとえ鋼種、板厚、電極条件などに変
化があったとしても溶接部の品質を安定して良好に保て
る点にある。上記第３、第４の発明と同様に溶接中の溶
接部温度を数値計算によって求めているので、後通電中
の溶接部の温度をオンラインで知ることができる。計算
によって求めた後通電中の溶接部の最高到達温度が、予
め定めた所定温度範囲内に入るように後通電電流と後通
電時間を調整する。これにより、電極劣化が起こった場
合であっても後通電中の溶接部の最高到達温度を良好な
範囲内に保持することができ、結果として高強度鋼板の
スポット溶接において溶接部の安定した良好な品質を確
保することが可能になる。In the present invention, the current is temporarily stopped after the welding current is completed, and then the post-current is started during the cooling, and thereafter the tempering process is performed on the welded portion by the current application. A feature of the present invention is that the post-energization current and the post-energization time are adjusted based on the temperature calculation result, so that the maximum welded temperature at the time of post-energization can be kept within a predetermined temperature range. As a result, even if there is a change in steel type, plate thickness, electrode conditions, and the like, the quality of the welded portion can be stably maintained well. Since the temperature of the welded portion during welding is obtained by numerical calculation as in the third and fourth aspects, the temperature of the welded portion during post-energization can be known online. The post-energization current and the post-energization time are adjusted such that the maximum temperature of the welded portion during energization obtained after the calculation falls within a predetermined temperature range. As a result, even when electrode deterioration occurs, the maximum attainable temperature of the welded portion during post-energization can be maintained within a good range, and as a result, the stable and good welded portion is obtained in spot welding of high-strength steel sheets. Quality can be ensured.
【００２８】本発明の第６は、高強度鋼板のスポット溶
接方法において、スポット溶接時の電流と電極間電圧を
計測し、計測した電流と電極間電圧および材料物性値を
用いて熱伝導モデルに基づいた数値計算からスポット溶
接部の任意の位置における各時刻毎の温度を求め、前記
求めた温度に基づいて電極加圧力を調整することを特徴
とする高強度鋼板のスポット溶接方法である。加圧力の
調整は、溶接通電後の温度下降時にスポット溶接部の特
定の位置における前記温度が予め定めた所定温度に到達
したら電極加圧力を増大させるように行うと好ましい。
スポット溶接部の特定の位置はナゲット端部から熱影響
部端部までの位置であり、予め定めた所定温度は２５０
〜４００℃とするとより好ましい（請求項２、９、１
１）。According to a sixth aspect of the present invention, in a spot welding method for a high-strength steel sheet, a current and a voltage between electrodes during spot welding are measured, and a heat conduction model is formed using the measured current, a voltage between electrodes, and material properties. A spot welding method for a high-strength steel plate, characterized in that a temperature at each time at an arbitrary position of a spot welded portion is obtained from a numerical calculation based on the calculated temperature, and an electrode pressing force is adjusted based on the obtained temperature. It is preferable that the adjustment of the pressing force is performed such that the electrode pressing force is increased when the temperature at a specific position of the spot weld reaches a predetermined temperature at the time of the temperature decrease after the welding current is applied.
The specific position of the spot weld is a position from the end of the nugget to the end of the heat-affected zone.
To 400 ° C. is more preferable.
1).
【００２９】スポット溶接部の十字引張強さや疲労強度
を改善する手段として、溶接部、特に熱影響部に圧縮の
残留応力を発生させることも有効である。上記第６の発
明は、スポット溶接後に電極の加圧力を調整し、これに
よって溶接部に圧縮の残留応力を発生させることを特徴
とする。熱影響部に有効に圧縮応力を残留させるために
は、溶接後の冷却中で溶融部が凝固しマルテンサイト変
態が終了した時点で電極加圧力を増加させることが特に
有効である。これにより、弾性歪みが導入され、圧縮の
残留応力がかかるものである。As a means for improving the cross tensile strength and fatigue strength of the spot weld, it is also effective to generate compressive residual stress in the weld, especially in the heat affected zone. The sixth aspect of the present invention is characterized in that the pressure of the electrode is adjusted after the spot welding, thereby generating a compressive residual stress in the welded portion. In order to effectively leave a compressive stress in the heat-affected zone, it is particularly effective to increase the electrode pressing force at the time when the molten zone solidifies during the cooling after welding and the martensitic transformation ends. Thereby, elastic strain is introduced, and compressive residual stress is applied.
【００３０】上記第６の発明では、熱伝導モデルに基づ
いた温度を求め、この温度に基づいて電極加圧力を調整
するので、たとえ電極が経時変化を起こしても的確なタ
イミングで電極加圧力の調整を行うことができる。In the sixth aspect of the present invention, the temperature is obtained based on the heat conduction model, and the electrode pressing force is adjusted based on this temperature. Therefore, even if the electrode changes with time, the electrode pressing force can be adjusted at an appropriate timing. Adjustments can be made.
【００３１】上記第６の発明は、第４の発明（溶接通電
後の後通電による冷却速度の緩和）、第５の発明（溶接
通電し冷却した後の後通電によるテンパー処理）と同時
に行うこともできる（請求項１０、１１）。これによ
り、溶接部の硬さが低下すると同時に熱影響部に圧縮応
力を残留させるので、十字引張強さや疲労強度はより一
層改善される。The sixth invention is performed simultaneously with the fourth invention (relaxation of cooling rate by post-energization after welding energization) and the fifth invention (tempering by post-energization after welding energization and cooling). (Claims 10 and 11). Thereby, the compressive stress remains in the heat-affected zone at the same time as the hardness of the welded portion is reduced, so that the cross tensile strength and the fatigue strength are further improved.
【００３２】本発明のスポット溶接方法に用いる好まし
い高強度鋼板は、下記の成分範囲に有り、引張強さが４
２０ＭＰａ以上１２００ＭＰａ以下とする。 ０．２０≦Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋２Ｐ＋４Ｓ≦
０．６０ ただし、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓは、それぞれ鋼中にお
ける炭素、シリコン、マンガン、リン、イオウの含有量
（質量％）である。The preferred high-strength steel sheet used in the spot welding method of the present invention has the following component range and a tensile strength of 4
20 MPa or more and 1200 MPa or less. 0.20 ≦ C + Si / 30 + Mn / 20 + 2P + 4S ≦
0.60 where C, Si, Mn, P and S are the contents (% by mass) of carbon, silicon, manganese, phosphorus and sulfur in the steel, respectively.
【００３３】[0033]
【発明の実施の形態】スポット溶接の連続打点を行なっ
た場合、電極先端の鋼板との接触面の状況が変化し、電
極と鋼板との接触面積が変化する。接触面積の変化は、
鋼板中における溶接電流の通電直径すなわち通電面積の
変化をもたらす。通電直径が変化すれば、たとえ溶接電
流として一定の電流を流したとしても、鋼板中における
通電部の電流密度が変化して発熱量が変化し、また発熱
部位が変化する。このような発熱状況の変化は、通電電
流を観察しているのみではキャッチすることができない
が、通電電流と共に電極間電圧を観察することによって
状況をキャッチすることが可能になる。即ち、通電電流
と電極間電圧とから電極間抵抗Ｒを求めることができ、
電極間抵抗と鋼板の板厚、固有抵抗から通電面積Ｓを求
めることができるのである。そして、これらの値を用い
ることによって、鋼板中の通電部位における単位体積あ
たりの発熱量を求めることができる。従って、溶接通電
中の通電電流と電極間電圧とを計測することにより、電
極と鋼板、鋼板同士の接触状況をある程度推定すること
ができる。BEST MODE FOR CARRYING OUT THE INVENTION When continuous spot welding of spot welding is performed, the condition of the contact surface of the electrode tip with the steel plate changes, and the contact area between the electrode and the steel plate changes. The change in contact area is
This results in a change in the diameter of the welding current, that is, the area of the welding current in the steel sheet. If the energized diameter changes, even if a constant current is applied as the welding current, the current density of the energized portion in the steel sheet changes, and the calorific value changes, and the heat generation site changes. Such a change in the heat generation state cannot be caught only by observing the energizing current, but it is possible to catch the situation by observing the inter-electrode voltage together with the energizing current. That is, the interelectrode resistance R can be obtained from the energizing current and the interelectrode voltage,
The current-carrying area S can be obtained from the inter-electrode resistance, the thickness of the steel sheet, and the specific resistance. Then, by using these values, it is possible to determine the heat value per unit volume at the energized portion in the steel sheet. Therefore, by measuring the current flowing during welding and the voltage between the electrodes, the contact state between the electrode and the steel plate or between the steel plates can be estimated to some extent.
【００３４】上記第１の発明は、この計算結果を用いる
ことを特徴とする。この推定結果に基づいて電極を鋼板
から離す時期の決定、溶接通電終了後に継続する後通電
における後通電電流と後通電時間の調整、溶接通電が終
了した後冷却しその後開始した後通電における後通電電
流と後通電時間の調整、電極加圧力の調整のうちの１又
は２以上を行えば、たとえ電極の経時変化があってもそ
の経時変化に対応して溶接時の熱履歴条件を一定に保つ
ことが可能であり、溶接品質を安定して良好に保つこと
ができる。The first invention is characterized in that the result of the calculation is used. Based on this estimation result, determine the timing of separating the electrode from the steel plate, adjust the post-energization current and post-energization time in the post-energization that continues after the end of welding energization, cool after the welding energization ends, and then start after energization. If one or more of the adjustment of the current and the post-energization time and the adjustment of the electrode pressing force are performed, even if the electrode changes with time, the heat history condition at the time of welding is kept constant corresponding to the change with time. It is possible to stably maintain good welding quality.
【００３５】次に、上記第２の発明における熱伝導モデ
ルに基づいた数値計算について説明する。熱伝導モデル
においては、鋼板中の発熱、鋼板中の熱伝導、鋼板から
電極への熱伝達、鋼板から外気への熱伝達に関してモデ
ルを作成し数値計算を行なう。鋼板から電極への熱伝達
に関しては、鋼板と電極との接触面積が、上記において
求めた通電面積Ｓに基づいて定めることができるので、
熱伝導モデルに組み込むことが可能になる。鋼板中の熱
伝導、鋼板から外気への熱伝達は一般的なモデルを用い
ることができ、鋼板中の発熱は通電面積に依存するが、
上記のようにこれは通電電流と電極間電圧とから求めら
れるので、全体としての熱伝導モデルを構築することが
可能である。この熱伝導モデルに基づいた数値計算によ
り、溶接部の任意の位置における各時刻毎の温度を求め
ることができる。Next, numerical calculation based on the heat conduction model in the second invention will be described. In the heat conduction model, a model is created and numerically calculated for heat generation in the steel sheet, heat conduction in the steel sheet, heat transfer from the steel sheet to the electrode, and heat transfer from the steel sheet to the outside air. Regarding heat transfer from the steel plate to the electrode, since the contact area between the steel plate and the electrode can be determined based on the energized area S obtained above,
It can be incorporated into a heat conduction model. A general model can be used for heat conduction in the steel sheet and heat transfer from the steel sheet to the outside air, and the heat generation in the steel sheet depends on the energized area,
As described above, since this is obtained from the supplied current and the voltage between the electrodes, it is possible to construct a heat conduction model as a whole. By a numerical calculation based on this heat conduction model, the temperature at each time at an arbitrary position of the welded portion can be obtained.
【００３６】スポット溶接においては、通常は５０Ｈｚ
又は６０Ｈｚの交流電流を印加して行なう。通電中にお
いて、交流電流の半サイクルにおいて通電電流と電極間
電圧との測定を行ない、残り半サイクルにおいて上記熱
伝導モデルに基づいた数値計算を行なって溶接部の任意
の位置における温度を求めることができる。最近のコン
ピュータの能力の向上に伴い、以上のような熱伝導計算
を交流電流の半サイクル内に実行することについては困
難性はない。In spot welding, usually 50 Hz
Alternatively, it is performed by applying an alternating current of 60 Hz. During energization, it is possible to measure the energizing current and the voltage between the electrodes in a half cycle of the alternating current, and perform a numerical calculation based on the heat conduction model in the remaining half cycle to obtain the temperature at an arbitrary position of the welded portion. it can. With the recent improvement in computer capabilities, there is no difficulty in performing such heat transfer calculations within a half cycle of alternating current.
【００３７】以上に述べた熱伝導モデルに基づく数値計
算は、従来、スポット溶接におけるナゲット径を制御す
る目的で使用されていた。例えば、溶接学会誌第６７巻
第４号第４５ページ〜第４９ページに開示されていると
おりである。本第２の発明においては、この熱伝導モデ
ルに基づく数値計算を、溶接後の溶接部温度履歴の制
御、あるいは溶接後の電極加圧力制御に適用したところ
に最大の特徴がある。Numerical calculations based on the heat conduction model described above have been used for the purpose of controlling the nugget diameter in spot welding. For example, as disclosed in the Journal of the Japan Welding Society, Vol. 67, No. 4, pp. 45-49. The second aspect of the present invention is characterized in that the numerical calculation based on this heat conduction model is applied to control of a weld temperature history after welding or to electrode pressure control after welding.
【００３８】上記第３の発明について説明する。第３の
発明においては、通電完了後の電極保持時間を短くする
ことによって溶接部の硬さを低下させ、高強度鋼板のス
ポット溶接部の品質を改善する。通電完了後の電極保持
時間を一定とするのではなく、溶接通電終了後の冷却中
において、温度計算結果に基づいて電極を鋼板から離す
時期を定めることが特徴である。The third invention will be described. In the third invention, the hardness of the welded portion is reduced by shortening the electrode holding time after the completion of the energization, and the quality of the spot welded portion of the high-strength steel plate is improved. Instead of keeping the electrode holding time after the energization is completed, it is characterized in that during cooling after the end of the welding energization, the timing of separating the electrode from the steel sheet is determined based on the temperature calculation result.
【００３９】連続打点によって電極状況が変化した場
合、従来のように電極保持時間を一定に保っていたので
は、電極保持中の鋼板急冷時の冷却到達温度が打点毎に
変化することとなり、電極を離したときにナゲットが完
全に凝固していない場合には、ナゲット部から溶融金属
が飛び出すトラブルが発生し、冷却到達温度が低すぎる
と溶接部の硬さが上昇して品質が低下することとなる。
本発明においては、電極を離すタイミングにおける溶接
部温度を常に適正に保つことができるので、これら従来
における問題点が発生することがない。In the case where the electrode condition changes due to continuous hitting, if the electrode holding time is kept constant as in the prior art, the ultimate cooling temperature during rapid cooling of the steel sheet while holding the electrode will change for each hitting point. If the nugget is not completely solidified when it is released, there is a problem that the molten metal jumps out of the nugget, and if the cooling temperature is too low, the hardness of the weld increases and the quality decreases. Becomes
In the present invention, since the temperature of the welded portion at the timing when the electrodes are separated can always be properly maintained, these conventional problems do not occur.
【００４０】上記第３の発明において温度計算結果に基
づいて電極を鋼板から離す時期を定めるに際しては、好
ましくは、計算によって求めた溶接部の所定位置におけ
る温度が所定温度より低下した時点で電極を鋼板から離
す。溶接部の特定位置として、通常はナゲット中心部を
選択するのが望ましく、電極を鋼板から離す所定温度と
して鋼板の凝固温度を選択するとより好ましい。電極保
持は、ナゲットの全体が凝固するまで行なっていればよ
い。ナゲット中では通常はナゲット中心部の温度が最も
高いので、ナゲット中心部の温度が鋼板の凝固温度より
低くなった時点が、ナゲットの全体が凝固した時点に一
致するのである。この時点で電極を鋼板から離せば、ナ
ゲットから溶鋼が飛散することもなく、冷却速度が速す
ぎて溶接部の硬さを上昇させることもない。一方、ナゲ
ットの中で最も温度の高い部分がナゲット中心部ではな
い場合もあるので、ナゲット中の全部位における温度が
凝固温度より低くなった時点で電極を鋼板から離すよう
に調整を行なえば、最も確実である。In the third aspect of the present invention, when determining the timing for separating the electrode from the steel sheet based on the temperature calculation result, preferably, the electrode is turned off when the calculated temperature at the predetermined position of the welded portion falls below the predetermined temperature. Remove from steel plate. Usually, it is desirable to select the central portion of the nugget as the specific position of the welded portion, and it is more preferable to select the solidification temperature of the steel plate as the predetermined temperature at which the electrode is separated from the steel plate. The electrode may be held until the entire nugget is solidified. In the nugget, since the temperature of the central portion of the nugget is usually the highest, the time when the temperature of the central portion of the nugget becomes lower than the solidification temperature of the steel plate coincides with the time when the entire nugget has solidified. If the electrode is separated from the steel plate at this time, the molten steel does not scatter from the nugget, and the cooling rate is not too fast to increase the hardness of the welded portion. On the other hand, since the highest temperature part of the nugget may not be the nugget center part, if the adjustment is performed so that the electrode is separated from the steel sheet when the temperature in all parts in the nugget becomes lower than the solidification temperature, Most sure.
【００４１】上記第４の発明について説明する。第４の
発明においては、溶接通電終了後も後通電を継続し、溶
接終了後の溶接部の冷却速度を緩冷却とする。さらに、
後通電電流と後通電時間を一定とするのではなく、温度
計算結果に基づいて後通電電流と後通電時間を調整す
る。The fourth invention will be described. In the fourth invention, the post-energization is continued even after the end of the energization of the welding, and the cooling rate of the welded portion after the end of the welding is set to slow cooling. further,
The post-energization current and the post-energization time are not fixed, but the post-energization current and the post-energization time are adjusted based on the temperature calculation result.
【００４２】溶接通電終了後の冷却時における計算温度
に基づいた後通電電流と後通電時間の調整は、スポット
溶接部の特定の位置における計算冷却時間が予め定めた
冷却時間範囲となるように後通電電流と後通電時間を調
整すると好ましい。計算によって求めた冷却時間が適正
冷却時間範囲よりも短ければ後通電電流と後通電時間を
増加し、逆であれば後通電電流と後通電時間を減少する
調整を行なう。このような調整の結果、溶接通電終了後
の溶接部の冷却時間は常に一定の適正な範囲に保たれ、
溶接部の品質を良好に保持することができる。The adjustment of the post-energization current and the post-energization time based on the calculated temperature at the time of cooling after the end of the welding energization is performed so that the calculated cooling time at a specific position of the spot welding portion is within a predetermined cooling time range. It is preferable to adjust the energizing current and the post-energizing time. If the calculated cooling time is shorter than the proper cooling time range, the post-current and post-current are increased, and if the cooling time is the opposite, the post-current and post-current are decreased. As a result of such an adjustment, the cooling time of the welded portion after the end of the welding energization is always kept within a certain appropriate range,
Good quality of the weld can be maintained.
【００４３】溶接通電終了後の冷却時における計算温度
に基づいた後通電電流と後通電時間の調整は、溶接部の
良好な品質を得ることのできる溶接部の適正な温度降下
速度（冷却速度）を予め確認しておいてもよい。実際の
溶接において、上記第３の発明と同様に、電流値、電極
間電圧の実績に基づいて熱伝導モデルに基づいた数値計
算を行ない、溶接部の温度を求める。溶接通電終了後の
後通電電流と後通電時間は、計算で求めた溶接部の温度
降下速度が該適正な温度降下速度になるように調整す
る。Adjustment of the post-energization current and the post-energization time based on the calculated temperature at the time of cooling after the end of the welding energization is performed by appropriately setting the temperature drop rate (cooling rate) of the welded portion so that good quality of the welded portion can be obtained. May be checked in advance. In the actual welding, as in the third invention, a numerical calculation based on a heat conduction model is performed based on the results of the current value and the inter-electrode voltage to determine the temperature of the welded portion. The post-energization current and the post-energization time after the end of the welding energization are adjusted so that the calculated temperature drop rate of the welded portion becomes the appropriate temperature drop rate.
【００４４】後通電電流と後通電時間の調整に関して
は、適正な温度降下速度を範囲で定めておいてもよい。
計算で求めた温度降下速度が適正範囲を下回った場合に
後通電電流と後通電時間を減少し、計算で求めた温度降
下速度が適正範囲を上回った場合には後通電電流と後通
電時間を増大する。このような調整により、実績の温度
降下速度を常に適正な範囲内におさめておくことが可能
になる。Regarding the adjustment of the post-energization current and the post-energization time, an appropriate temperature drop rate may be determined in a range.
If the calculated temperature drop rate falls below the appropriate range, reduce the post-current and post-current time.If the calculated temperature drop rate exceeds the appropriate range, reduce the post-current and post-current time. Increase. Such adjustment makes it possible to keep the actual temperature drop rate within an appropriate range.
【００４５】冷却時間や温度降下速度を求めるスポット
溶接部の特定の位置は、図１においてナゲット端部１０
から熱影響部端部１１までの位置とするとより好まし
い。十字引張強さの測定において、破壊の起点になるの
はナゲット端部１０から熱影響部端部１１までの位置で
ある。疲労破壊の起点も同様の場所である。従って、こ
の部分の強度や靭性を改善することが溶接部の品質向上
に最も寄与する。また、予め定めた冷却時間範囲は凝固
温度から１０００℃までの冷却時間が溶接時間の６０％
以上の範囲とするとより好ましい。適正冷却時間を範囲
で規定する場合には、凝固温度から１０００℃までの冷
却時間が溶接時間の６０〜１００％である。溶接時間の
６０％未満となると、冷却速度が速すぎて溶接部の元素
の偏析が緩和されず、十字引張強さや疲労強度が低下す
ることとなる。一般的に、ナゲット内と熱影響部では、
Ｓｉ、Ｍｎ、Ｐ、Ｓなどの偏析が認められるが、Ｃｅｑ
が高い場合にはこの偏析が顕著となり、十字引張強さは
低下する。しかし、冷却速度を緩和し１０００℃以上で
の保持時間を長くすることによって拡散が起こり、この
偏析が緩和され十字引張強さは向上するのである。一
方、溶接時間の１００％を超えると、冷却時間が長くな
りすぎ、溶接生産性を低下させることとなるからであ
る。The specific positions of the spot welds for which the cooling time and the temperature drop rate are to be obtained are shown in FIG.
It is more preferable to set the distance from the heat-affected zone end 11. In the measurement of the cross tensile strength, the starting point of the fracture is the position from the nugget end 10 to the heat-affected zone end 11. The starting point of fatigue failure is the same place. Therefore, improving the strength and toughness of this portion most contributes to improving the quality of the welded portion. The predetermined cooling time range is that the cooling time from the solidification temperature to 1000 ° C. is 60% of the welding time.
It is more preferable to set the above range. When the appropriate cooling time is specified in the range, the cooling time from the solidification temperature to 1000 ° C. is 60 to 100% of the welding time. If the welding time is less than 60%, the cooling rate is too high, segregation of elements in the welded portion is not alleviated, and the cross tensile strength and fatigue strength decrease. Generally, in the nugget and in the heat affected zone,
Although segregation of Si, Mn, P, S, etc. is observed, Ceq
Is high, this segregation becomes remarkable, and the cross tensile strength decreases. However, diffusion occurs when the cooling rate is relaxed and the holding time at 1000 ° C. or higher is extended, and this segregation is relaxed and the cross tensile strength is improved. On the other hand, if it exceeds 100% of the welding time, the cooling time becomes too long, and the welding productivity is reduced.
【００４６】上記第５の発明について説明する。第５の
発明においては、溶接通電終了後に一度電流を停止し、
次いで冷却後に後通電を開始し、この後通電によって溶
接部にテンパー処理を施す。さらに、計算温度に基づい
て後通電電流と後通電時間を調整するので、後通電時の
溶接部最高到達温度を所定の温度範囲内におさめること
が可能になる。The fifth invention will be described. In the fifth invention, the current is stopped once after the welding energization is completed,
Next, after the cooling, post-energization is started, and thereafter, the welding portion is subjected to a tempering treatment by the energization. Furthermore, since the post-energization current and the post-energization time are adjusted based on the calculated temperature, it is possible to keep the maximum weld temperature at the time of post-energization within a predetermined temperature range.
【００４７】後通電電流と後通電時間の調整は、最も簡
単には、後通電による溶接部の温度上昇時において、目
標温度に到達した時点で通電を終了する方法を採用する
ことができる。さらに、後通電時の溶接部の温度計算結
果から温度上昇速度を求め、温度上昇速度が適正値より
も速ければ後通電電流を減少し、温度上昇速度が適正値
よりも遅ければ後通電電流を増加するという調整方法を
採用することも可能である。The simplest adjustment of the post-energization current and the post-energization time can employ a method in which the energization is terminated when the target temperature is reached when the temperature of the welded portion is increased by the post-energization. Further, the temperature rise speed is calculated from the result of the temperature calculation of the welded portion at the time of post-energization, and if the temperature rise speed is faster than an appropriate value, the post-energization current is decreased. It is also possible to adopt an adjustment method of increasing.
【００４８】溶接通電を完了してから後通電を開始する
までの通電停止期間は、冷却中の熱影響部の温度を計算
し、マルテンサイト変態が終了（温度として４００℃以
下程度）するまでの時間として定める。後通電の最適条
件は、何種類かの後通電電流と後通電時間を用いて後通
電を行ない、溶接部の品質評価によって最適な後通電条
件を定めることができる。このとき、熱伝導モデルによ
る数値計算で溶接部の温度を求めておく。このようにし
て、品質を改善する観点から最適な後通電の最高到達温
度を定めることができる。During the power supply stop period from the completion of the welding power supply to the start of the post-power supply, the temperature of the heat-affected zone during cooling is calculated, and the time until the martensitic transformation ends (about 400 ° C. or less as a temperature) is calculated. Set as time. The optimum conditions for the post-energization can be determined by performing post-energization using several types of post-energization currents and post-energization times, and determining the optimal post-energization conditions by evaluating the quality of the welded portion. At this time, the temperature of the welded portion is obtained by numerical calculation using a heat conduction model. In this way, the highest post-energization maximum temperature that is optimal from the viewpoint of improving quality can be determined.
【００４９】最適な後通電の最高到達温度を定めるべき
溶接部の特定の位置としては、上記第４の発明と同様、
ナゲット端部１０から熱影響部端部１１までの位置とす
ることが好ましい。理由は第４の発明で説明したとおり
である。また、最高到達温度の範囲は５００〜９００℃
とすると好ましい。５００℃未満では熱影響部のマルテ
ンサイトが十分焼戻されなくて硬さが下がらず、９００
℃を超えるとオーステナイト域に入って再度冷却中にマ
ルテンサイト変態が起こるからである。The specific position of the welded portion at which the optimum maximum temperature of the post-energization should be determined is the same as in the fourth invention.
It is preferable to set the position from the nugget end 10 to the heat-affected zone end 11. The reason is as described in the fourth invention. The maximum temperature range is 500-900 ° C
Is preferable. If the temperature is lower than 500 ° C., the martensite in the heat-affected zone is not sufficiently tempered and the hardness does not decrease.
If the temperature exceeds ℃, martensitic transformation occurs during the austenite region and cooling again.
【００５０】後通電終了後の電極保持を選択することに
よって、後通電終了後の冷却速度を調整することもでき
る。本第３の発明と同様、電極保持時間の調整を熱伝導
モデルに基づく温度計算結果によって行っても良い。By selecting the electrode holding after the post-energization, the cooling rate after the post-energization can be adjusted. Similarly to the third aspect, the adjustment of the electrode holding time may be performed based on a temperature calculation result based on a heat conduction model.
【００５１】上記第６の発明について説明する。第６の
発明は、スポット溶接後に電極の加圧力を調整し、これ
によって溶接部に圧縮の残留応力を発生させる。熱影響
部に有効に圧縮応力を残留させるためには、溶接後の冷
却中で溶融部が凝固しマルテンサイト変態が終了した時
点で電極加圧力を増加させることが特に有効である。電
極加圧力を増加させるタイミングは、冷却中においてナ
ゲット端部から熱影響部端部までの位置の温度が２５０
〜４００℃に到達した時点とすると好ましい。電極加圧
力増加タイミングが４００℃を超えているとマルテンサ
イト変態が完全に終了しておらず、２５０℃未満では十
分な弾性歪が入らないからである。また、電極加圧力
は、溶接時の１．２〜１．６倍の範囲とすると好まし
い。１．２倍未満だと十分な弾性歪が入らず、１．６倍
以上だと溶接部の圧痕が深くなって外観を損ねたり、板
厚が薄くなって継手強度が低下するからである。The sixth invention will be described. According to a sixth aspect of the present invention, after the spot welding, the pressure of the electrode is adjusted, thereby generating a compressive residual stress in the welded portion. In order to effectively leave a compressive stress in the heat-affected zone, it is particularly effective to increase the electrode pressing force at the time when the molten zone solidifies during the cooling after welding and the martensitic transformation ends. The timing for increasing the electrode pressure is such that the temperature at the position from the end of the nugget to the end of the heat-affected zone during cooling is 250 ° C.
It is preferable to reach the point when the temperature reaches to 400 ° C. This is because the martensitic transformation is not completely completed when the electrode pressing force increase timing exceeds 400 ° C., and sufficient elastic strain is not applied at less than 250 ° C. Further, it is preferable that the electrode pressing force be in a range of 1.2 to 1.6 times the welding pressure. If it is less than 1.2 times, sufficient elastic strain will not be applied, and if it is 1.6 times or more, indentation of the welded portion will be deep and the appearance will be damaged, and the plate thickness will be reduced and the joint strength will be reduced.
【００５２】本発明の上記１〜６に用いる高強度鋼板と
しては、下記の成分範囲に有り、引張強さが４２０ＭＰ
ａ以上１２００ＭＰａ以下とすると好適である。 ０．２０≦Ｃｅｑ＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋２Ｐ
＋４Ｓ≦０．６０ ただし、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓは、それぞれ鋼中にお
ける炭素、シリコン、マンガン、リン、イオウの含有量
（質量％）である。The high-strength steel sheet used in the above 1 to 6 of the present invention has the following component range and a tensile strength of 420 MPa.
It is preferable that the pressure is not less than a and not more than 1200 MPa. 0.20 ≦ Ceq = C + Si / 30 + Mn / 20 + 2P
+ 4S ≦ 0.60 where C, Si, Mn, P, and S are the contents (% by mass) of carbon, silicon, manganese, phosphorus, and sulfur in the steel, respectively.
【００５３】Ｃｅｑが０．２０未満であるときは硬さが
問題とはならず、０．６０を超えると本発明方法でも十
字引張強さ、疲労強度の改善を得ることができないから
である。また、同じく、引張強さが４２０ＭＰａ未満で
あるときは硬さが問題とはならず、１２００ＭＰａを超
えると本発明方法でも十字引張強さ、疲労強度の改善を
得ることができないからである。When Ceq is less than 0.20, hardness does not matter, and when it exceeds 0.60, improvement in cross tensile strength and fatigue strength cannot be obtained even by the method of the present invention. Similarly, when the tensile strength is less than 420 MPa, hardness is not a problem, and when it exceeds 1200 MPa, the cross tensile strength and the fatigue strength cannot be improved even by the method of the present invention.
【００５４】本発明で用いる高強度鋼板は、引張強さが
４２０ＭＰａ以上１２００ＭＰａ以下である鋼板ならば
特に限定するものではなく、固溶強化型、析出強化型
（Ｔｉ析出型、Ｎｂ析出型）、２相組織型（フェライト
中にマルテンサイトを含む組織、あるいはフェライト中
にベイナイトを含む組織）、加工誘起変態型（フェライ
ト中に残留オーステナイトを含む組織）、などいずれの
タイプの鋼板であっても良い。板厚については、一般的
に自動車などで使う鋼板の板厚、例えば、０．４ｍｍ〜
４．０ｍｍ程度で良い。鋼板の製造方法は、熱間圧延法
でも冷間圧延法でも良い。The high-strength steel sheet used in the present invention is not particularly limited as long as the steel sheet has a tensile strength of 420 MPa or more and 1200 MPa or less, and may be a solid solution strengthening type, a precipitation strengthening type (Ti precipitation type, Nb precipitation type), Any type of steel sheet, such as a two-phase structure type (a structure containing martensite in ferrite or a structure containing bainite in ferrite) or a work-induced transformation type (a structure containing residual austenite in ferrite), may be used. . About the thickness, the thickness of a steel sheet generally used in automobiles, for example, 0.4 mm to
It may be about 4.0 mm. The method for producing the steel sheet may be a hot rolling method or a cold rolling method.
【００５５】ナゲットを形成させるスポット溶接条件、
すなわち電極形状、電極加圧力、溶接電流、溶接時間
は、一般のスポット溶接条件に準ずれば良い。Spot welding conditions for forming a nugget,
That is, the electrode shape, electrode pressing force, welding current, and welding time may be in accordance with general spot welding conditions.
【００５６】熱伝導モデルによる数値計算は、溶接通電
完了後の冷却やテンパー通電の制御に用いるのみでな
く、溶接通電そのものの制御に用いてもよい。これによ
り、電極使用回数が増大して電極の劣化が起こった場合
においても、ナゲット径を常に一定に保つことができ
る。The numerical calculation using the heat conduction model may be used not only for controlling the cooling and the tempering current after the welding current is completed but also for controlling the welding current itself. Thereby, even when the number of times of use of the electrode is increased and the electrode is deteriorated, the nugget diameter can always be kept constant.
【００５７】[0057]
【実施例】図２は、本実施例で用いたスポット溶接方法
を説明するための図である。図２に示したように、被溶
接材である２枚の高強度鋼板１を重ね合わせ、銅電極４
で加圧しながら通電し、２枚の高強度鋼板の間に溶融部
を形成させ、通電終了後、溶融部を凝固させてナゲット
２を形成させスポット溶接する。この際、図２で示した
ように、溶接中の電流と電極間電圧（銅電極４の間の電
圧）を計測装置５で測定し、これを使って発熱、熱伝導
計算を演算装置６で実施し、任意の位置における各時刻
の温度変化を算出し、これを基に、制御装置７で電流、
溶接時間、加圧力を制御できるようになっている。FIG. 2 is a diagram for explaining the spot welding method used in this embodiment. As shown in FIG. 2, two high-strength steel sheets 1 to be welded are overlapped, and a copper electrode 4
Is applied while pressurizing to form a fusion zone between the two high-strength steel sheets. After the energization, the fusion zone is solidified to form the nugget 2 and spot welded. At this time, as shown in FIG. 2, the current during welding and the voltage between the electrodes (the voltage between the copper electrodes 4) are measured by the measuring device 5, and using this, heat generation and heat conduction calculation are performed by the arithmetic device 6. The temperature change at each time at an arbitrary position is calculated, and based on the calculated temperature change,
Welding time and pressure can be controlled.
【００５８】（実施例１）本第３の発明を用いて高強度
鋼板のスポット溶接を行なった。被溶接材として、板
厚：１．２ｍｍ、引張強さ：８１２ＭＰａの加工誘起変
態型複合組織高強度鋼板（記号：７８０Ｔ）と、比較材
として板厚が同一で引張強さが３６２ＭＰａの軟鋼板
（記号：ＳＰＨＣ）を用いた。(Example 1) Spot welding of a high-strength steel sheet was performed using the third invention. As a material to be welded, a high-strength steel plate (symbol: 780T) of a work-induced transformation composite structure having a thickness of 1.2 mm and a tensile strength of 812 MPa, and a mild steel plate having the same thickness and a tensile strength of 362 MPa as a comparative material (Symbol: SPHC) was used.
【００５９】まず、電極保持を解除する適正な溶接部温
度を確認するための試験を行なった。First, a test was conducted to confirm an appropriate welding temperature for releasing the electrode holding.
【００６０】スポット溶接継手の引張試験方法（ＪＩＳ
Ｚ３１３７）に基づいて十字引張試験片を作製し、ス
ポット溶接時の電流と電極間電圧を計測しながら、これ
らを表１に示した条件（ナゲット径が５.５ｍｍになる
条件）でスポット溶接した。溶接時に、計測した電流と
電極間電圧から、計算機シミュレーションによってナゲ
ット中央部の温度を計算で求めた。図３には、条件２〜
５について、ナゲット中央部の温度の推移を図示した。
通電終了後から電極を離すまでの時間を保持時間とする
と、表１に示したように、ナゲット中央部の凝固が終了
した後に電極を離した条件１と２（保持時間：６０、１
００ｍｓ）では、７８０Ｔ溶接継手の十字引張強さはＳ
ＰＨＣ溶接継手（条件７と８）と同レベルであった。一
方、凝固が終了しても電極を離さず保持時間を長くした
条件３と４（保持時間：３００、５００ｍｓ）では、７
８０Ｔ溶接継手の十字引張強さはＳＰＨＣ溶接継手（条
件７と８）より低い値を示した。また、ナゲット中央部
で凝固が終了していない条件５と６（保持時間：０、２
０ｍｓ）では、溶融部が鋼板間から飛散してナゲット内
に欠陥が発生するため、７８０Ｔ溶接継手の十字引張強
さはＳＰＨＣ溶接継手（条件７と８）より低い値を示し
た。このように、ナゲット中央部の温度が凝固温度より
低くなった時点で電極保持を解除することにより、７８
０Ｔ溶接継手の十字引張強さをＳＰＨＣ溶接継手と同レ
ベルにすることが可能になった。他の鋼種あるいは板厚
を変化させて同様の実験を実施したが、結果は同様であ
った。[0060] Tensile test method for spot welded joints (JIS
Z3137), a cross-tension test specimen was prepared, and the spot welding was performed under the conditions shown in Table 1 (the conditions for the nugget diameter to be 5.5 mm) while measuring the current and the electrode voltage during spot welding. . During welding, the temperature at the center of the nugget was calculated by computer simulation from the measured current and the voltage between the electrodes. FIG. 3 shows conditions 2 to
With respect to No. 5, the transition of the temperature at the center of the nugget is illustrated.
Assuming that the time from the end of energization to the separation of the electrode is the holding time, as shown in Table 1, the conditions 1 and 2 for separating the electrode after the solidification of the central portion of the nugget were completed (holding time: 60, 1
00ms), the cross tensile strength of the 780T welded joint is S
It was at the same level as the PHC welded joint (conditions 7 and 8). On the other hand, under the conditions 3 and 4 (holding time: 300, 500 ms) in which the electrode was not released and the holding time was extended even after the coagulation was completed, 7
The cross tensile strength of the 80T welded joint was lower than that of the SPHC welded joint (conditions 7 and 8). Conditions 5 and 6 where coagulation was not completed at the center of the nugget (retention time: 0, 2
At 0 ms), the cross-tension strength of the 780T welded joint was lower than that of the SPHC welded joints (conditions 7 and 8) because the melted portion scattered from between the steel sheets and defects were generated in the nugget. As described above, by releasing the electrode holding when the temperature of the central portion of the nugget becomes lower than the solidification temperature, 78
The cross tensile strength of the 0T welded joint can be made the same level as that of the SPHC welded joint. Similar experiments were performed with other steel types or plate thicknesses changed, but the results were similar.
【００６１】[0061]
【表１】 [Table 1]
【００６２】次いで、連続打点時において本第３の発明
を適用した。溶接中においてナゲット中央部の温度を計
算によって求め、溶接完了後冷却中においてナゲット中
央部の温度が凝固温度より低くなった時点で電極保持を
解除することとした。電極使用初期においては、上記と
同様保持時間６０〜１００ｍｓであったものが、電極使
用回数が１５０００回を超えると、電極保持時間は８０
〜１２０ｍｓ程度となった。この場合においても、電極
保持解除時におけるナゲット中央部温度は凝固温度より
低いので、溶接部の十字引張り強度はＳＰＨＣ溶接継手
と同レベルであった。Next, at the time of continuous hitting, the third invention was applied. During the welding, the temperature at the center of the nugget was obtained by calculation, and after the welding was completed, the electrode holding was released when the temperature at the center of the nugget became lower than the solidification temperature during cooling. In the initial stage of the use of the electrode, the holding time was 60 to 100 ms in the same manner as described above.
It was about 120 ms. Also in this case, the temperature at the center of the nugget when the electrode was released was lower than the solidification temperature, so that the cross tensile strength of the welded portion was at the same level as that of the SPHC welded joint.
【００６３】比較例として、連続打点中常に電極保持時
間を１００ｍｓ一定としてスポット溶接を行なった。電
極使用回数が２００００回を超えると、７８０Ｔの十字
引張強さはＳＰＨＣの９０％程度と低い値を示した。As a comparative example, spot welding was performed with the electrode holding time kept constant at 100 ms during continuous hitting. When the number of times the electrode was used exceeded 20,000 times, the cross tensile strength at 780T showed a value as low as about 90% of SPHC.
【００６４】（実施例２）実施例１と同じ鋼板を用い、
本第４の発明を用いて高強度鋼板のスポット溶接を行な
った。まず、最適な冷却速度を確認するための試験を行
なった。同じナゲット径が得られる条件でスポット溶接
する際、表２に示したように、溶接後も一定時間一定の
電流を流しながら、溶接部各位置の温度変化を数値計算
で求めた。十字引張試験時に破断が起こる位置として、
図１のナゲット端部１０と熱影響部端部１１との間に位
置する熱影響部９の位置（より具体的にはボンドから熱
影響部側の半径方向０．２ｍｍの位置）での温度を求め
た。十字引張強さを測定した結果を表２に示す。図４に
は、条件２、４、６、７についての熱影響部９での温度
推移を示す。凝固温度から１０００℃までの冷却時間が
溶接時間の７１％である条件１と２では、７８０Ｔ溶接
継手の十字引張強さがＳＰＨＣ溶接継手（条件７）と同
レベルであったが、冷却時間がそれより短い条件３〜６
では、７８０Ｔ溶接継手の十字引張強さはＳＰＨＣ溶接
継手（条件７）より低い値を示した。即ち、最適な冷却
時間範囲は、凝固温度から１０００℃までの冷却時間が
溶接時間の６０％以上であることが判明した。Example 2 Using the same steel plate as in Example 1,
Using the fourth invention, spot welding of a high-strength steel plate was performed. First, a test was performed to confirm the optimum cooling rate. When spot welding was performed under the same nugget diameter condition, as shown in Table 2, a constant current was passed for a certain period of time after welding, and the temperature change at each position of the weld was determined by numerical calculation. As the position where the break occurs during the cross tension test,
The temperature at the position of the heat-affected zone 9 located between the nugget end 10 and the heat-affected zone end 11 in FIG. 1 (more specifically, at a position 0.2 mm in the radial direction from the bond to the heat-affected zone). I asked. Table 2 shows the results of measuring the cross tensile strength. FIG. 4 shows the temperature transition in the heat-affected zone 9 under the conditions 2, 4, 6, and 7. Under conditions 1 and 2 in which the cooling time from the solidification temperature to 1000 ° C. was 71% of the welding time, the cross tensile strength of the 780T welded joint was at the same level as that of the SPHC welded joint (condition 7). Shorter conditions 3-6
The cross tensile strength of the 780T welded joint was lower than that of the SPHC welded joint (condition 7). That is, it was found that the optimum cooling time range was that the cooling time from the solidification temperature to 1000 ° C. was 60% or more of the welding time.
【００６５】[0065]
【表２】 [Table 2]
【００６６】次いで、連続打点時において本発明を適用
した。後通電中に温度計算結果から求めた温度降下速度
が適正な温度降下速度以上になった場合には後通電電流
を増大し、適正な温度降下速度以下になった場合には後
通電電流を減少する調整を行なった。電極使用回数が１
５０００回を超えて電極先端径が増加した電極を用いた
場合でも、７８０Ｔ溶接継手の十字引張強さをＳＰＨＣ
溶接継手と同レベルにすることが可能になった。他の鋼
種あるいは板厚を変化させて同様の実験を実施したが、
結果は同様であった。電極使用回数が増大するにつれ、
後通電電流が増大する傾向が見られた。Next, the present invention was applied at the time of continuous hitting. If the temperature drop rate obtained from the temperature calculation results during the post-energization is higher than the appropriate temperature drop rate, the post-current is increased, and if it is lower than the appropriate temperature drop, the post-current is decreased. Adjustments were made. 1 use of electrode
Even when an electrode whose electrode tip diameter has increased more than 5000 times is used, the cross tensile strength of the 780T welded joint is determined by SPHC.
It is now possible to achieve the same level as welded joints. A similar experiment was performed with other steel types or plate thicknesses changed.
The results were similar. As the number of electrode usage increases,
There was a tendency for the post-current to increase.
【００６７】比較例として、連続打点中常に冷却時の後
通電電流を５．１ｋＡ一定としてスポット溶接を行なっ
た。後通電を行わない場合よりは改善されているもの
の、電極使用回数が増大すると品質改善効果が徐々に失
われた。As a comparative example, spot welding was performed at a constant post-conduction current of 5.1 kA during cooling during continuous hitting. Although the quality was improved as compared with the case where the post-energization was not performed, the quality improvement effect was gradually lost as the number of use of the electrodes increased.
【００６８】（実施例３）実施例１と同じ鋼板を用い、
本第５の発明を用いて高強度鋼板のスポット溶接を行な
った。まず、後通電時の適正な最高到達温度を定めるた
めのテストを行なった。同じナゲット径が得られる条件
でスポット溶接する際、表３に示したように、溶接後５
００ｍｓ通電を休止して溶接部を冷却した後再度通電し
て、十字引張試験時に破断が起こる位置として図１の熱
影響部９（ボンドから熱影響部側の半径方向０．２ｍｍ
の位置）での温度を求めた。十字引張強さを測定した結
果を表３に示す。図５には、条件１、２についての熱影
響部９の温度推移を示す。熱影響部９での最高到達温度
が７００〜８５０℃になる条件１と２では、７８０Ｔ溶
接継手の十字引張強さがＳＰＨＣ溶接継手（条件５）と
同レベルであったが、それより低いあるいは高くなる条
件３と４では、７８０Ｔ溶接継手の十字引張強さがＳＰ
ＨＣ溶接継手（条件５）より低い値を示した。即ち、熱
影響部９における最高到達温度が７００〜８５０℃にな
るように電流と通電時間を設定すると好ましいことが判
明した。Example 3 Using the same steel plate as in Example 1,
Using the fifth invention, spot welding of a high-strength steel plate was performed. First, a test was performed to determine an appropriate maximum temperature at the time of post-energization. When spot welding under the same nugget diameter condition, as shown in Table 3,
After the current was stopped for 00 ms, the weld was cooled and then energized again, and the heat-affected zone 9 of FIG.
At the position). Table 3 shows the results of measuring the cross tensile strength. FIG. 5 shows the temperature transition of the heat-affected zone 9 under the conditions 1 and 2. Under conditions 1 and 2 where the maximum temperature reached in the heat-affected zone 9 is 700 to 850 ° C., the cross tensile strength of the 780T welded joint was at the same level as the SPHC welded joint (condition 5), but was lower or lower. Under conditions 3 and 4, the cross tensile strength of the 780T welded joint is SP
The value was lower than that of the HC welded joint (condition 5). That is, it has been found that it is preferable to set the current and the conduction time so that the maximum temperature in the heat-affected zone 9 is 700 to 850 ° C.
【００６９】[0069]
【表３】 [Table 3]
【００７０】次に連続打点時に本発明を実施した。電極
使用回数が１５０００回を超え、電極先端径が増加した
電極を用いた場合でも、熱影響部における温度計算結果
に基づいて最高到達温度を調整することによって、７８
０Ｔ溶接継手の十字引張強さをＳＰＨＣ溶接継手と同レ
ベルにすることが可能になった。他の鋼種あるいは板厚
を変化させて同様の実験を実施したが、結果は同様であ
った。Next, the present invention was carried out at the time of continuous hitting. Even when the number of electrode usage exceeds 15,000 times and an electrode with an increased electrode tip diameter is used, by adjusting the maximum attainable temperature based on the temperature calculation result in the heat-affected zone, 78
The cross tensile strength of the 0T welded joint can be made the same level as that of the SPHC welded joint. Similar experiments were performed with other steel types or plate thicknesses changed, but the results were similar.
【００７１】比較例として、後通電電流を５．１ｋＡ一
定、後通電時間を２８０ｍｓ一定として連続打点を行な
った。その結果、連続打点の増加と共に７８０Ｔの十字
引張強さはＳＰＨＣの十字引張強さより低下した。As a comparative example, continuous spotting was performed with the post-energization current constant at 5.1 kA and the post-energization time constant at 280 ms. As a result, the cross tensile strength at 780 T was lower than the cross tensile strength of SPHC as the number of continuous hit points increased.
【００７２】（実施例４）被溶接材として、板厚：１．
６ｍｍ、引張強さ：４５２ＭＰａの固溶強化型高強度鋼
板（記号：４４０Ｓ）と、板厚が同一で引張強さが３７
２ＭＰａの軟鋼板（記号：ＳＰＨＣ）を用い、本第５の
発明を実施した。(Example 4) As a material to be welded, a plate thickness: 1.
6mm, tensile strength: 452MPa solid solution strengthened high-strength steel sheet (symbol: 440S), the same plate thickness and tensile strength of 37
The fifth invention was implemented using a 2 MPa mild steel plate (symbol: SPHC).
【００７３】スポット溶接継手の疲れ試験方法（ＪＩＳ
Ｚ３１３８）に基づいて引張せん断疲労試験片を作製
した。これらを表４に示した条件（ナゲット径が６.３
ｍｍになる条件）で通電し、５００ｍｓ通電を休止して
溶接部を冷却した後再度通電した。図６には、条件１、
２、４についての熱影響部９の温度推移を示す。これら
の継手について、引張せん断疲労試験法（ＪＩＳ Ｚ３
１３８）に基づいて疲労試験を実施した。疲労試験は片
振り試験で行い、応力比；０．０５、周波数；３０Ｈｚ
の条件で行った。２×１０6回における疲労強度を表４
に示す。図１の熱影響部９（ボンドから熱影響部側の半
径方向０．２ｍｍの位置）での最高到達温度が７５０〜
８５０℃になるように電流と通電時間を設定した条件１
と２では、溶接後再通電しない場合（条件６）に比べて
疲労強度は向上し、これは、ＳＰＨＣ溶接継手（条件
７）の疲労強度よりも高い値であった。一方、熱影響部
９での最高到達温度がそれより低いあるいは高い条件３
と４の場合には、疲労強度は向上していなかった。即
ち、疲労試験時に破断が起こる熱影響部９での計算最高
到達温度が７５０〜８５０℃になるように電流と通電時
間を設定すると好適であることが判明した。Fatigue test method for spot welded joints (JIS
Z3138) to produce a tensile shear fatigue test specimen. These were measured under the conditions shown in Table 4 (when the nugget diameter was 6.3).
mm), the power supply was stopped for 500 ms, and the welded portion was cooled and then supplied with electricity again. FIG. 6 shows condition 1,
The temperature transition of the heat affected zone 9 for 2 and 4 is shown. For these joints, tensile shear fatigue test method (JIS Z3
138) based on the fatigue test. The fatigue test was performed by a swing test, stress ratio: 0.05, frequency: 30 Hz
Was performed under the following conditions. Table 4 shows the fatigue strength at 2 × 10 6 times.
Shown in The maximum temperature reached in the heat-affected zone 9 (the position 0.2 mm in the radial direction from the bond to the heat-affected zone) in FIG.
Condition 1 in which current and energizing time are set to be 850 ° C
In (2) and (3), the fatigue strength was improved as compared with the case where no re-energization was performed after welding (condition 6), which was higher than the fatigue strength of the SPHC welded joint (condition 7). On the other hand, the condition 3 where the maximum temperature reached in the heat-affected zone 9 is lower or higher
In cases 4 and 4, the fatigue strength was not improved. In other words, it has been found that it is preferable to set the current and the conduction time so that the highest calculated temperature in the heat-affected zone 9 at which the fracture occurs during the fatigue test is 750 to 850 ° C.
【００７４】[0074]
【表４】 [Table 4]
【００７５】次に連続打点時に本発明を実施した。電極
先端径が増加した電極を用いた場合でも、熱影響部での
温度変化を推定し、熱影響部における最高到達温度が上
記と同じになるように電流と通電時間を制御することに
よって、４４０Ｓの疲労強度を溶接のみの試験片より向
上させることが可能になった。他の鋼種あるいは板厚を
変化させて同様の実験を実施したが、結果は同様であっ
た。Next, the present invention was implemented at the time of continuous hitting. Even when an electrode having an increased electrode tip diameter is used, by estimating the temperature change in the heat-affected zone and controlling the current and the conduction time so that the maximum attained temperature in the heat-affected zone becomes the same as described above, 440S It has become possible to improve the fatigue strength of the test piece compared to the test piece using only welding. Similar experiments were performed with other steel types or plate thicknesses changed, but the results were similar.
【００７６】（実施例５）本第６の発明を実施した。被
溶接材として、板厚：１．６ｍｍ、引張強さ：５９４Ｍ
Ｐａの加工誘起変態型複合組織鋼板（５９０Ｔ）を用い
た。スポット溶接継手の疲れ試験方法（ＪＩＳＺ３１３
８）に基づいて引張せん断疲労試験片を作製した。これ
らを表５の条件１に示した条件（ナゲット径が６.３ｍ
ｍになる条件）で通電した。この際、計測した電流と電
極間電圧から、計算機シミュレーションによって図１の
熱影響部９（ボンドから熱影響部側の半径方向０．２ｍ
ｍの位置）での温度変化を推定し、溶接後の冷却中にお
けるその位置での温度が２５０〜４００℃になった時点
で電極加圧力を１．４倍に増加させた。これらの継手に
ついて、引張せん断疲労試験法（ＪＩＳＺ３１３８）に
基づいて疲労試験を実施した。疲労試験条件は第４の実
施例と同じである。２×１０6回における疲労強度を表
５に示す。電極荷重を１．４倍に向上させた条件１で
は、電極荷重を増加させない条件２やＳＰＨＣの条件３
に比べて疲労強度は向上した。(Embodiment 5) The sixth invention is implemented. As a material to be welded, plate thickness: 1.6 mm, tensile strength: 594M
A work-induced transformation type composite structure steel sheet (590T) of Pa was used. Fatigue test method for spot welded joints (JISZ313
A tensile shear fatigue test piece was prepared based on 8). These were measured under the conditions shown in condition 1 of Table 5 (the nugget diameter was 6.3 m).
m). At this time, from the measured current and the voltage between the electrodes, the heat-affected zone 9 in FIG.
The temperature change at the position (m position) was estimated, and when the temperature at that position during cooling after welding became 250 to 400 ° C., the electrode pressing force was increased by 1.4 times. These joints were subjected to a fatigue test based on a tensile shear fatigue test method (JISZ3138). The fatigue test conditions are the same as in the fourth embodiment. Table 5 shows the fatigue strength at 2 × 10 6 times. In the condition 1 in which the electrode load was increased by a factor of 1.4, the condition 2 in which the electrode load was not increased and the condition 3 in the SPHC were not increased.
The fatigue strength was improved as compared with.
【００７７】[0077]
【表５】 [Table 5]
【００７８】次に連続打点時に本発明を実施した。電極
先端径が増加した電極を用いた場合でも、熱影響部での
温度変化を推定し、熱影響部における最高到達温度が上
記と同じになるように電流と通電時間を制御することに
よって、５９０Ｔの疲労強度を溶接のみの試験片より向
上させることが可能になった。他の鋼種あるいは板厚を
変化させて同様の実験を実施したが、結果は同様であっ
た。Next, the present invention was implemented at the time of continuous hitting. Even when an electrode having an increased electrode tip diameter is used, a temperature change in the heat-affected zone is estimated, and the current and the conduction time are controlled so that the maximum temperature reached in the heat-affected zone is the same as described above. It has become possible to improve the fatigue strength of the test piece compared to the test piece using only welding. Similar experiments were performed with other steel types or plate thicknesses changed, but the results were similar.
【００７９】[0079]
【発明の効果】本発明は、高強度鋼板のスポット溶接方
法において、スポット溶接時の電流と電極間電圧を計測
し、計測した電流と電極間電圧および材料物性値を用い
た数値計算を行い、溶接終了後の冷却中に前記計算結果
に基づいて、電極を鋼板から離す時期の決定、溶接通電
終了後に継続する後通電における後通電電流と後通電時
間の調整、溶接通電を終了した後冷却しその後開始した
後通電における後通電電流と後通電時間の調整、電極加
圧力の調整のうちの１又は２以上を行うことにより、た
とえ電極の経時変化があっても溶接品質（溶接部の十字
引張強さ、疲労強度等）を安定して良好に保つことがで
きるようになった。計測した電流と電極間電圧および材
料物性値を用いた数値計算は、熱伝導モデルに基づいた
数値計算によりスポット溶接部の任意の位置における各
時刻毎の温度を求める数値計算を行えば、溶接品質の安
定性をより一層高めることができる。According to the present invention, in a spot welding method for a high-strength steel sheet, a current and a voltage between electrodes at the time of spot welding are measured, and a numerical calculation is performed using the measured current, a voltage between electrodes, and material properties. During the cooling after welding, based on the above calculation result, the timing of separating the electrode from the steel plate, the adjustment of the post-current and post-current time in the post-current that is continued after the end of welding, and cooling after the end of welding. By performing one or more of the adjustment of the post-energization current and the post-energization time in the post-energization after starting, and the adjustment of the electrode pressing force, even if the electrode changes with time, the welding quality (cross tension of the welded portion) Strength, fatigue strength, etc.) can be maintained stably and favorably. Numerical calculations using the measured current, electrode voltage, and material property values can be performed by numerical calculation based on the heat conduction model to calculate the temperature at each point in the spot weld at each point in time. Can be further enhanced in stability.
【００８０】本発明は、特に溶融浸漬法、電気めっき法
などで製造されためっき鋼板（Ｚｎめっき、Ｚｎ−Ｆｅ
めっき、Ｚｎ−Ａｌめっき、Ｎｉ−Ｚｎめっき、Ｓｎ−
Ｚｎめっき、Ｐｂ−Ｓｎめっき、など）を行なった高強
度鋼板のスポット溶接において大きな効果を発揮する。
めっき鋼板を連続打点する場合には、打点数の増加に伴
ってめっき部と電極との合金化反応が起こり、打点数の
増加に伴い電極先端の劣化が特に急速に進行するためで
ある。The present invention is particularly applicable to plated steel sheets (Zn plating, Zn-Fe
Plating, Zn-Al plating, Ni-Zn plating, Sn-
It exerts a great effect in spot welding of a high-strength steel sheet which has been subjected to Zn plating, Pb-Sn plating, etc.).
This is because, when a plated steel sheet is continuously hit, an alloying reaction occurs between the plated portion and the electrode as the number of hit points increases, and the electrode tip deteriorates particularly rapidly with an increase in the number of hit points.
【図１】スポット溶接部の疲労試験時における破壊を説
明するための断面図である。FIG. 1 is a cross-sectional view for explaining destruction of a spot weld at the time of a fatigue test.
【図２】本発明におけるスポット溶接方法を説明するた
めの断面図である。FIG. 2 is a cross-sectional view illustrating a spot welding method according to the present invention.
【図３】本発明の実施例１におけるナゲット中心部の数
値計算による温度推移を示す図である。FIG. 3 is a diagram showing a temperature transition by numerical calculation of a central portion of a nugget according to the first embodiment of the present invention.
【図４】本発明の実施例２における熱影響部の数値計算
による温度推移を示す図である。FIG. 4 is a diagram showing a temperature transition by numerical calculation of a heat-affected zone in Embodiment 2 of the present invention.
【図５】本発明の実施例３における熱影響部の数値計算
による温度推移を示す図である。FIG. 5 is a diagram showing a temperature transition by numerical calculation of a heat-affected zone in Embodiment 3 of the present invention.
【図６】本発明の実施例４における熱影響部の数値計算
による温度推移を示す図である。FIG. 6 is a diagram showing a temperature transition by numerical calculation of a heat-affected zone in Embodiment 4 of the present invention.
１ 高強度鋼板 ２ ナゲット ３ 負荷方向 ４ 銅電極 ５ 計測装置 ６ 演算装置 ７ 制御装置 ８ ナゲット中心部 ９ 熱影響部 １０ ナゲット端部 １１ 熱影響部端部 DESCRIPTION OF SYMBOLS 1 High-strength steel plate 2 Nugget 3 Load direction 4 Copper electrode 5 Measuring device 6 Computing device 7 Control device 8 Nugget center 9 Heat affected zone 10 Nugget end 11 Heat affected zone end
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｂ６２Ｄ 65/00 Ｂ６２Ｄ 65/00 Ｑ (72)発明者 田中 隆 富津市新富20−１ 新日本製鐵株式会社技 術開発本部内 (72)発明者 小原 昌弘 大分市大字西ノ州１番地 新日本製鐵株式 会社大分製鐵所内 Ｆターム(参考） 3D114 AA20 BA01 CA05 EA04 ──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. 7 Identification symbol FI Theme coat ゛ (Reference) B62D 65/00 B62D 65/00 Q (72) Inventor Takashi Tanaka 20-1 Shintomi, Futtsu Nippon Steel Corporation (72) Inventor Masahiro Ohara 1 Oshino-shi, Oita-shi Nippon Steel Corporation F-term in Oita Works (reference) 3D114 AA20 BA01 CA05 EA04
Claims (12)
て、スポット溶接時の電流と電極間電圧を計測し、計測
した電流と電極間電圧および材料物性値を用いた計算を
行い、溶接通電終了後の冷却中に前記計算結果に基づい
て、電極を鋼板から離す時期の決定、溶接通電終了後に
継続する後通電における後通電電流と後通電時間の調
整、溶接通電を終了した後冷却しその後開始した後通電
における後通電電流と後通電時間の調整、電極加圧力の
調整のうちの１又は２以上を行うことを特徴とする高強
度鋼板のスポット溶接方法。In a spot welding method for a high-strength steel sheet, a current and a voltage between electrodes at the time of spot welding are measured, a calculation is performed using the measured current, a voltage between electrodes, and a material property value. Based on the calculation results during cooling, based on the calculation result, determine the timing of separating the electrode from the steel sheet, adjust the post-current and post-current time in post-current, which continues after the end of welding current, after cooling and start after finishing welding current A spot welding method for a high-strength steel sheet, wherein one or two or more of adjustment of a post-energization current and a post-energization time in energization and adjustment of an electrode pressing force are performed.
料物性値を用いた計算は、熱伝導モデルに基づいた数値
計算によりスポット溶接部の任意の位置における各時刻
毎の温度を求める数値計算であることを特徴とする請求
項１に記載の高強度鋼板のスポット溶接方法。2. The calculation using the measured current, inter-electrode voltage, and material property values is performed by numerical calculation based on a heat conduction model to obtain a temperature at an arbitrary position of a spot weld at each time. The spot welding method for a high-strength steel sheet according to claim 1, wherein:
度に基づいて電極を鋼板から離す時期を定める請求項２
に記載の高強度鋼板のスポット溶接方法において、電極
を鋼板から離す時期の決定については、溶接通電終了後
の冷却中にスポット溶接部の特定の位置における前記温
度が予め定めた所定温度より低くなったら電極を鋼板か
ら離すことを特徴とする高強度鋼板のスポット溶接方
法。3. A timing for separating the electrode from the steel sheet based on the determined temperature during cooling after the completion of welding power supply.
In the spot welding method for a high-strength steel sheet according to the above, with respect to the determination of the time to separate the electrode from the steel sheet, the temperature at a specific position of the spot welded portion is lower than a predetermined temperature during cooling after the end of welding power supply. A spot welding method for high-strength steel sheets, wherein the electrodes are separated from the steel sheets.
ット中心部であり、予め定めた所定温度は鋼板の凝固温
度であることを特徴とする請求項３に記載の高強度鋼板
のスポット溶接方法。4. The spot welding method for a high-strength steel plate according to claim 3, wherein the specific position of the spot weld is a center portion of the nugget, and the predetermined temperature is a solidification temperature of the steel plate. .
中に前記求めた温度に基づいて後通電電流と後通電時間
を調整する請求項２に記載の高強度鋼板のスポット溶接
方法において、前記求めた温度に基づいた後通電電流と
後通電時間の調整は、スポット溶接部の特定の位置にお
ける冷却時間が予め定めた冷却時間範囲となるように後
通電電流と後通電時間を調整することを特徴とする高強
度鋼板のスポット溶接方法。5. The spot welding method for a high-strength steel sheet according to claim 2, wherein the post-energization is continued even after the end of the welding energization, and the post-energization current and the post-energization time are adjusted based on the determined temperature during cooling. The adjustment of the post-energization current and the post-energization time based on the obtained temperature is performed by adjusting the post-energization current and the post-energization time so that the cooling time at a specific position of the spot welding portion is within a predetermined cooling time range. A spot welding method for a high strength steel sheet.
ット端部から熱影響部端部までの位置であり、予め定め
た冷却時間範囲は凝固温度から１０００℃までの冷却時
間が溶接時間の６０％以上となる範囲であることを特徴
とする請求項５に記載の高強度鋼板のスポット溶接方
法。6. A specific position of the spot weld is a position from an end of the nugget to an end of the heat-affected zone, and a predetermined cooling time range is such that the cooling time from the solidification temperature to 1000 ° C. is 60 times the welding time. The spot welding method for a high-strength steel sheet according to claim 5, wherein the amount is in a range of not less than%.
通電を開始し、前記求めた温度に基づいて後通電電流と
後通電時間を調整する請求項２に記載の高強度鋼板のス
ポット溶接方法において、前記求めた温度に基づいた後
通電電流と後通電時間の調整は、スポット溶接部の特定
の位置における前記計算最高到達温度が予め定めた所定
温度範囲内に入るように後通電電流と後通電時間を調整
することを特徴とする高強度鋼板のスポット溶接方法。7. The spot welding of a high-strength steel sheet according to claim 2, wherein after the energization of the welding is completed, cooling is performed, then the energization is started, and the post-energization current and the post-energization time are adjusted based on the determined temperature. In the method, the adjustment of the post-energization current and the post-energization time based on the determined temperature includes the post-energization current and the post-energization current such that the calculated maximum attained temperature at a specific position of the spot weld falls within a predetermined temperature range. A spot welding method for a high-strength steel sheet, wherein a post-energization time is adjusted.
ット端部から熱影響部端部までの位置であり、予め定め
た所定温度範囲は５００〜９００℃であることを特徴と
する請求項７に記載の高強度鋼板のスポット溶接方法。8. A specific position of the spot weld is a position from an end of the nugget to an end of the heat-affected zone, and a predetermined temperature range is 500 to 900 ° C. The spot welding method for a high-strength steel sheet according to item 1.
調整する請求項２に記載の高強度鋼板のスポット溶接方
法において、前記求めた温度に基づいた加圧力の調整
は、溶接通電終了後の温度降下時にスポット溶接部の特
定の位置における前記温度が予め定めた所定温度に到達
したら電極加圧力を増大させることを特徴とする高強度
鋼板のスポット溶接方法。9. The method for spot welding a high-strength steel sheet according to claim 2, wherein the electrode pressing force is adjusted based on the determined temperature. A spot welding method for a high-strength steel plate, wherein the electrode pressing force is increased when the temperature at a specific position of the spot weld reaches a predetermined temperature at the time of the temperature drop.
て、スポット溶接時の電流と電極間電圧を計測し、計測
した電流と電極間電圧および材料物性値を用いて熱伝導
モデルに基づいた数値計算からスポット溶接部の任意の
位置における各時刻毎の温度を求め、溶接通電終了後の
温度降下時にスポット溶接部の特定の位置における前記
温度が予め定めた所定温度に到達したら電極加圧力を増
大させることを特徴とする請求項５乃至８のいずれかに
記載の高強度鋼板のスポット溶接方法。10. In a spot welding method for a high-strength steel sheet, a current and a voltage between electrodes during spot welding are measured, and a numerical calculation based on a heat conduction model is performed using the measured current, a voltage between electrodes, and material properties. Obtaining the temperature at each time at an arbitrary position of the spot welded portion, and increasing the electrode pressing force when the temperature at a specific position of the spot welded portion reaches a predetermined temperature at the time of the temperature drop after the end of the welding energization. The spot welding method for a high-strength steel sheet according to any one of claims 5 to 8, characterized in that:
ゲット端部から熱影響部端部までの位置であり、予め定
めた所定温度は２５０〜４００℃であることを特徴とす
る請求項９又は１０に記載の高強度鋼板のスポット溶接
方法。11. A specific position of the spot welded portion is a position from an end of a nugget to an end of a heat affected zone, and the predetermined temperature is 250 to 400 ° C. 11. The spot welding method for a high-strength steel sheet according to 10.
有り、引張強さが４２０ＭＰａ以上１２００ＭＰａ以下
であることを特徴とする請求項１乃至１１のいずれかに
記載の高強度鋼板のスポット溶接方法。 ０．２０≦Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋２Ｐ＋４Ｓ≦
０．６０ ただし、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓは、それぞれ鋼中にお
ける炭素、シリコン、マンガン、リン、イオウの含有量
（質量％）である。12. The spot welding of a high-strength steel sheet according to claim 1, wherein the high-strength steel sheet has the following component range, and has a tensile strength of 420 MPa or more and 1200 MPa or less. Method. 0.20 ≦ C + Si / 30 + Mn / 20 + 2P + 4S ≦
0.60 where C, Si, Mn, P, and S are the contents (% by mass) of carbon, silicon, manganese, phosphorus, and sulfur in the steel, respectively.
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